PNITEBSITY  OF   CALIFORNIA   PUBLICATION 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


THE   EVAPORATION   OF 
GRAPES 


BY 

W.  V.  CRUESS,    A.  W.  CHRISTIE 

AND 

F.  C.  H.  FLOSSFEDER 


BULLETIN  No.  322 

June,  1920 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY 

1920 


David  P.  Barrows,  President  of  the  University. 


EXPERIMENT  STATION  STAFF 

HEADS  OF  DIVISIONS 

Thomas  Forsyth  Hunt,  Dean. 

Edward  J.  Wickson,  Horticulture  (Emeritus). 

Walter  Mulford,  Forestry,  Director  of  Resident  Instruction. 

Herbert  J.  Webber,  Director  Agricultural  Experiment  Station. 

B.  H.  Crocheron,  Director  of  Agricultural  Extension. 
Hubert  E.  Van  Norman,  Vice-Director;  Dairy  Management. 

James  T.  Barrett,  Acting  Director  of  Citrus  Experiment  Station;  Plant  Pathology 
William  A.  Setchell,  Botany 
Myer  E.  Jaffa  Nutrition. 
Charles  W.  Woodworth,  Entomology. 
Ralph  E.  Smith,  Plant  Pathology. 
J.  Eliot  Coit,  Citriculture. 
John  W.  Gilmore,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 
John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Fruit  Products. 
Warren  T.  Clarke,  Agricultural  Extension. 
John  S.  Burd,  Agricultural  Chemistry. 
Charles  B.  Lipman,  Soil  Chemistry  and  Bacteriology 
Clarence  M.  Haring,  Veterinary  Science. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
Fritz  W.  Woll,  Animal  Nutrition. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Reed,  Plant  Physiology. 
L.  D.  Batchelor,  Orchard  Management. 
J.  C.  Whitten,  Pomology, 
t Frank  Adams,  Irrigation  Investigations. 

C.  L.  Roadhouse,  Dairy  Industry. 
R.  L.  Adams,  Farm  Management. 

F.  L.  Griffin,  Agricultural  Education. 
John  E.  Dougherty,  Poultry  Husbandry. 
L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Voorhies,  Assistant  to  the  Dean. 

fin  co-operation  with  office  of  Public  Roads  and  Rural  Engineering,  U.  S.  Department  of  Agriculture 


THE   EVAPORATION   OF  GRAPES 

BY 
W.  V.  CRUESS,  A.  W.  CHRISTIE,  and  F.  C.  FLOSSFEDER 


CONTENTS 

PAGE 

I.     Purpose  of  Investigation 421 

II.     Acknowledgments '. 422 

III.  Principles  of  Evaporation 423 

(a)    Necessity  of  Heat 423 

(6)    Modes  of  Conveying  Heat 424 

(c)  Necessity  of  Air  Circulation 424 

(d)  Humidity  Control 425 

(e)  Miscellaneous  Requirements 427 

IV.  The  University  Farm  Evaporator 428 

(a)   List  of  Materials  and  Cost  of  Construction 428 

(6)    Description  of  the  Evaporator  Used  in  1919 430 

(c)    Course  followed  by  Grapes  at  Evaporator 434 

id)   Suggested  Revisions  in  Plan  of  University  Farm  Evaporator 436 

V.  Cost  of  Operation 441 

VI.  Results  of  Investigations 442 

(a)   Dipping 442 

(6)    Sun  Drying  vs.  Evaporation 447 

(c)    Sulfuring 450 

id)   Effect  of  Temperature  on  Quality  and  Rate  of  Drying 451 

(e)    Effect  of  Construction  of  Trays 452 

(/)    Comparison  of  Gravity  and  Air  Blast  Burner 455 

ig)    Comparison  of  Disc  and  Multivane  Fans 456 

ih)   Exhaust  vs.  Positive  Blower  Fan 458 

ii)    Recirculation  of  Air 459 

ij)    Direct  Use  of  Gases  of  Combustion  in  Drying 461 

ik)   Moisture  Content  of  Evaporated  Grapes 463 

(Z)    The  Determination  of  Humidity 465 

(m)  Measurement  of  Air  Velocity 467 

in)  Experiments  on  Stemming,  Seeding,  and  Packing 467 

VII.  Summary 469 

I.      PURPOSE    OF    THE    INVESTIGATION 

Drying  has  proved  to  be  one  of  the  most  feasible  methods  of 
converting  the  wine  grapes  of  California  into  a  non-perishable  salable 
product.  In  the  hot  interior  valleys,  where  the  grapes  ripen  early, 
the  fruit  may  be  dried  successfully  on  field  trays  in  the  vineyard. 


422  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

However,  at  least  50  per  cent  of  the  wine  grapes  are  grown  in  regions 
where  the  grapes  ripen  so  late  that  sun-drying  can  not  be  safely 
undertaken,  because  of  the  danger  of  loss  through  early  fall  rains. 

In  the  raisin-growing  districts,  serious  loss  from  early  rains  to  Sul- 
tanina  and  Muscat  grapes  on  drying  trays  has  occurred  several  times 
during  the  past  ten  years.  Some  provision  should  also  be  made  for 
utilizing  the  second-crop  Muscat  grapes  which  in  former  years  have 
been  sold  to  wineries  and  distilleries.  These  grapes  ripen  too  late  in 
the  fall  to  permit  of  drying  them  in  the  sun.  In  the  aggregate,  they 
amount  to  many  thousand  tons,  and  formerly  were  a  source  of  con- 
siderable revenue  to  the  raisin  growers. 

The  cull  Tokay  and  other  cull  table  grapes  from  the  packing  houses 
and  the  inferior  bunches  left  on  the  vines  have  been  used  principally 
for  wine  making  in  past  years.  Much  of  the  brandy  used  in  the 
manufacture  of  sweet  wine  was  made  from  this  cull  fruit  and  resulted 
in  a  small  return  to  the  grower. 

It  is  contended  by  many  that  a  greater  yield  and  a  better  quality 
of  raisins  are  obtained  by  artificial  drying  in  an  evaporator  than  in 
the  sun. 

Because  of  these  important  reasons  it  is  imperative  that  there  be 
available  for  producers  of  all  varieties  of  grapes  reliable  information 
on  the  construction  and  operation  of  evaporators  for  the  drying  of 
raisin  grapes,  wine  grapes,  cull  table  grapes,  and  second-crop  Muscats. 
The  investigations  recorded  in  this  publication  were  carried  out  for 
the  purpose  of  obtaining  such  information.  While  the  magnitude  of 
the  problem  has  made  its  completion  in  the  one  season's  time  devoted 
to  it  impossible,  we  believe  the  results  obtained  to  date  are  sufficiently 
important  and  conclusive  to  warrant  their  publication. 

Most  of  the  data  reported  were  obtained  in  the  commercial 
evaporator  at  the  University  Farm,  Davis,  although  a  great  many 
small-scale  experiments  were  made  in  our  experimental  evaporators 
at  Berkeley. 

II.      ACKNOWLEDGMENTS 

The  erection  of  an  evaporator  of  commercial  size  was  made  possible 
by  a  grant  of  $2500  from  the  State  Board  of  Viticultural  Commis- 
sioners with  which  the  equipment  and  most  of  the  building  materials 
for  the  evaporator  were  purchased. 

Through  the  courtesy  of  Dr.  J.  C.  Whitten  of  the  Division  of 
Pomology,  a  portion  of  the  Deciduous  Fruits  Appropriation  passed 
by  the  last  State  Legislature  was  applied  in  the  employment  of  a 


Bulletin  322  THE  EVAPORATION  OF  GRAPES  423 

chemist  who  cooperated  in  carrying  out  the  investigations.  "Without 
these  two  special  funds  very  little  investigational  work  could  have 
been  performed. 

The  writers  wish  to  thank  Professor  F.  T.  Bioletti  for  the  valu- 
able suggestions  given  during  the  planning  and  construction  of  the 
evaporator  and  during  the  investigations. 

III.      PRINCIPLES    OF    EVAPORATION 

The  construction  of  evaporators  and  the  discussion  of  the  experi- 
mental results  will  be  better  understood  if  the  more  important  prin- 
ciples and  previously  existing  data  on  fruit  evaporation.  Evaporators 
of  many  types  have  been  used  with  varying  degrees  of  success  for 
many  years.  From  the  experience  gained  in  the  use  of  these  evapor- 
ators and  from  observations  and  measurements  taken  by  scientific 
investigators  certain  principles  have  become  recognized.  To  this  exist- 
ing knowledge  new  information  is  being  constantly  added  and  some 
of  the  older  theories  are  being  discarded  or  seriously  modified. 

(a)   NECESSITY  OF  HEAT 

Evaporation  of  fruits  involves  the  change  of  water  from  the  liquid 
to  the  vapor  state.  This  change  requires  the  expenditure  of  a  very 
definite  amount  of  heat  regardless  of  the  system  of  evaporation  and 
the  temperature  used.  This  quanitity  of  heat  is  known  as  the  "latent 
heat  of  vaporization"  and  is  equal  to  the  amount  of  heat  given  off 
when  steam  condenses  to  water. 

Expressed  in  the  usual  heat-unit  terms,  approximately  965  British 
Thermal  Units  of  heat  are  required  to  evaporate  one  pound  of  water. 
A  British  Thermal  Unit  (B.  T.  U.)  is  the  amount  of  heat  used  in 
raising  one  pound  of  water  one  degree  Fahrenheit.  To  the  heat 
actually  used  in  evaporation  must  be  added  that  needed  to  raise  the 
fruit  from  its  original  temperature  to  that  of  the  evaporator.  This 
ordinarily  amounts  to  50  to  75  B.  T.  U.  per  pound  of  fruit;  thus 
making  the  total  minimum  quantity  of  heat  necessary  slightly  above 
1000  B.  T.  U.  per  pound  of  water  evaporated. 

The  fuel  efficiency  of  an  evaporator  may  be  judged  by  its  approach 
to  this  minimum  in  its  heat  requirements.  If  the  drying  ratio  of  the 
fruit,  the  weight  of  fruit  evaporated,  the  quantity  of  fuel  consumed, 
and  the  heat  value  of  the  fuel  are  known,  the  heat  efficiency  of  the 
evaporator  may  be  calculated.  In  most  evaporators  it  will  be  found 
that  not  over  50  per  cent  of  the  heat  generated  in  the  furnace  is 


424  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT    STATION 

utilized  in  drying  the  fruit  because  of  the  heat  lost  by  radiation  and 
leaks  in  the  evaporator  and  the  heat  lost  in  the  exhaust  air.  This  last 
loss  is  the  greatest.  A  typical  case  will  show  its  magnitude.  If  the 
outside  air  at  80°  F.  is  heated  to  160°  F.,  as  it  enters  the  evaporator, 
and  if  it  leaves  the  evaporator  at  120°  F.,  it  is  readily  seen  that  only 
40°  F.  of  the  80°  F.  rise  in  temperature  is  utilized,  or  less  than  50 
per  cent  of  the  heat  is  utilized  in  drying,  if  we  include  radiation  and 
other  minor  losses  of  heat. 

Many  evaporators  have  failed  because  they  have  not  been  supplied 
with  sufficient  heat.  The  air  heating  system  must  have  adequate 
capacity  and  should  supply  an  abundance  of  heat  without  the  need 
of  forcing  the  furnace.  The  attempt  to  force  the  furnace  beyond  its 
capacity  has  been  a  very  common  cause  of  loss  of  evaporators  by  fire. 

(ft)  MODES  OF  CONVEYING  HEAT 

Heat  may  be  applied  or  conveyed  to  the  fruit  in  several  ways.  It 
may  be  conducted  by  direct  contact  of  the  fruit  with  the  heating 
system.  This  method  of  conveying  the  heat  has  not  been  used  in 
practice  to  any  appreciable  extent  because  the  high  temperatures  of 
the  heating  element  would  scorch  the  fruit.  In  European  countries 
community  bake  ovens  are  often  used  for  drying  fruits  after  the 
bread  has  been  removed,  the  fruit  in  many  cases  resting  in  contact 
with  the  hot  bricks  of  the  oven. 

Heat  may  to  a  limited  degree  reach  the  fruit  by  radiation,  just 
as  heat  is  radiated  into  a  room  from  a  fire  place  or  stove.  In  the 
stack  and  tunnel  types  of  evaporators  it  is  probable  that  this  mode 
of  heat  transfer  is  of  appreciable  importance  but  in  the  average  air- 
blast  type  of  evaporator  it  is  negligible. 

By  far  the  most  important  method  of  heat  transfer  is  by  air 
currents,  which  may,  if  we  use  the  term  rather  loosely,  be  termed 
''transfer  of  heat  by  convection."  The  air  is  heated  by  contact  with 
a  furnace,  radiating  pipes,  or  other  heating  system,  and  the  heated  air 
rises  through  the  drying  compartment  because  it  is  lighter  than  the 
outside  air  or  it  is  transferred  over  the  fruit  to  be  dried  by  means 
of  a  fan. 

(c)   NECESSITY  OF  AIR  CIRCULATION 

Since  a  large  amount  of  heat  is  essential  for  successful  drying 
and  since  air  is  the  usual  vehicle  for  transfer  of  this  heat  from  the 
furnace  to  the  fruit  the  necessity  of  air  circulation  in  the  evaporator 


Bulletin  322  THE  EVAPORATION  OF  GRAPES  425 

can  be  seen.  Just  how  important  this  factor  is,  may  be  seen  from  the 
following  consideration.  It  will  require  approximately  63,000  cubic 
feet  of  air  dropping  one  degree  Fahrenheit  to  furnish  965  B.  T.  U., 
the  heat  necessary  to  evaporate  one  pound  of  water ;  or  it  will  require 
approximately  1575  cubic  feet  of  air  dropping  40°  F.  to  furnish  this 
amount  of  heat.  A  40°  F.  drop  in  temperature  is  probably  greater 
than  that  taking  place  in  the  average  evaporator;  consequently,  1575 
cubic  feet  of  air  per  pound  of  water  evaporated  may  be  considered 
in  the  nature  of  the  minimum  air  requirement.  An  evaporator 
holding  5  tons  of  grapes  which  dry  in  24  hours  and  which  have  a 
drying  ratio  of  3:1  must  evaporate  6666  pounds  of  water  per  24 
hours,  or  4.6  pounds  per  minute.  This  will  require  a  minimum  of 
4.6X1574  =  7245  cubic  feet  of  air  per  minute.  If  the  drying 
period  is  12  hours,  approximately  14,500  cubic  feet  of  air  per  minute 
will  be  needed.  A  few  evaporators  have  during  the  past  season  dried 
wine  grapes  in  twelve  hours  but  twenty-four  hours  time  or  longer 
was  required  in  most  cases.  In  our  small  evaporator  at  Berkeley 
which  was  supplied  with  an  excess  of  air,  grapes  were  dried  in  from 
six  to  twelve  hours,  indicating  the  possibilities  of  reducing  the  drying 
period  of  grapes  by  increasing  the  air  supply,  which  means  also 
increased  heat  supply. 

(d)   HUMIDITY  CONTEOL 

Air  circulation  is  also  important  as  a  means  of  carrying  away  the 
moisture  evaporated  from  the  fruit  by  the  heat.  In  a  "dead  air" 
space,  heated  fruit  for  a  short  time  rapidly  gives  up  its  moisture  to 
the  surrounding  air  which  soon  becomes  saturated  and  further 
evaporation  ceases  unless  the  saturated  air  is  replaced  by  fresh  dry 
air.  The  moisture-carrying  capacity  of  air  is  relatively  limited ;  hence, 
a  large  volume  of  air  must  pass  over  the  fruit  to  carry  away  the 
moisture  if  drying  is  to  be  continuous  and  rapid.  A  rough  conception 
of  the  amount  of  air  needed  for  this  purpose  under  average  conditions 
may  be  had  from  the  following  consideration. 

At  101°  F.,  approximately  350  cubic  feet  of  air  at  the  saturation 
point  is  required  to  carry  one  pound  of  water.  At  128°  F.,  this  same 
volume  of  air  will  hold  at  saturation  two  pounds  of  water  vapor, 
and  at  155°  F.,  four  pounds  of  water  vapor;  that  is  to  say,  each  27°  F. 
rise  in  temperature  will  double  the  moisture-absorbing  power  of  the 
air.  At  120°  F.,  350  cubic  feet  of  air  will  absorb  about  1%  pounds 
of  water  vapor. 


426  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

These  figures  refer  to  air  saturated  with  moisture  vapor;  that  is, 
air  of  100  per  cent  relative  humidity.  Relative  humidity  may  be 
defined  as  the  percentage  of  saturation  of  air  with  water  vapor, 
although  the  condition  applies  also  to  a  space  which  may  be  free 
from  air.  In  most  commercial  evaporators,  however,  we  are  dealing 
with  air. 

Few  evaporators  raise  the  relative  humidity  of  the  air  above  50 
per  cent.  If  the  air  leaves  the  evaporator  at  50  per  cent  relative 
humidity  and  at  120°  F.,  it  will  carry  approximately  1%  pounds  of 
water  vapor  per  350  cubic  feet  or  each  1000  cubic  feet  will  carry 
approximately  five  pounds  of  moisture.  For  an  evaporator  drying 
5  tons  of  grapes  per  24  hours,  approximately  5  pounds  of  water  must 
be  removed  from  the  grapes  per  minute,  or  at  least  1000  cubic  feet 
of  fresh  air  must  be  drawn  through  the  evaporator  per  minute  to 
carry  away  the  moisture. 

In  the  above  calculations  to  determine  the  amount  of  air  necessary 
to  carry  the  required  amount  of  heat  to  the  fruit  it  was  found  that 
approximately  7245  cubic  feet  of  air  per  minute  was  required.  Com- 
paring this  result  with  the  amount  of  air  needed  to  carry  away  the 
moisture  we  find  that  about  seven  times  as  much  air  is  needed  to  fur- 
nish heat  for  evaporation  as  is  necessary  to  carry  away  the  water 
evaporated  by  this  heat.  If  this  extra  six-sevenths  of  the  air  is  allowed 
to  escape,  much  fuel  value  and  much  of  the  moisture-carrying  capacity 
is  wasted.  If  six-sevenths  of  the  air  under  the  above  assumed  condi- 
tions be  returned  to  the  furnace  room  and  mixed  with  one-seventh  of 
fresh  air  and  if  one-seventh  of  this  mixture  after  reheating  and  passage 
through  the  evaporator  be  allowed  to  escape  at  50  per  cent  or  greater 
relative  humidity  it  is  readily  seen  that  the  efficiency  of  the  evaporator 
is  greatly  increased. 

This  recirculation  of  the  air  is  not  only  theoretically  more  efficient 
but  is  of  great  value  in  practice  for  other  reasons.  If  the  air  is  too 
dry  and  of  high  temperature,  moisture  may  be  taken  from  the  surface 
of  the  fruit  more  rapidly  than  it  can  effuse  from  the  interior,  resulting 
in  the  formation  of  a  hard  shell  on  the  surface,  or  ' '  case  hardening, ' ' 
which  retards  subsequent  evaporation.  If  the  humidity  of  the  air  is 
relatively  high,  diffusion  keeps  pace  with  evaporation  and  case  harden- 
ing is  prevented.  A  second  advantage  of  the  higher  humidity  of  the 
air  is  in  preventing  the  over-drying  of  fruit ;  because  drying  will  cease 
when  the  fruit  and  air  arrive  at  the  same  relative  moisture  content. 
Grapes  tend  to  dry  unevenly  and  many  to  over-dry  in  an  atmosphere 
of  very  low  humidity ;  that  is,  in  very  dry  hot  air.  A  third  advantage 
of  the  higher  humidity  is  its  tendency  to  reduce  the  injurious  effects 


Bulletin  322  THe  evaporation  OF  grapes  427 

of  high  temperatures  on  the  fruit  flavors.  It  is  therefore  possible  to 
use  higher  temperatures  of  drying  with  humid  air  than  with  dry  air. 

Because  of  the  vital  importance  of  controlling  the  humidity  of  the 
air  used  in  drying,  prospective  purchasers  and  manufacturers  of 
evaporators  are  advised  to  install  in  their  plants  some  means  of  effect- 
ively regulating  the  moisture  content  of  the  air.  One  of  the  most 
effective  methods  of  increasing  the  humidity  of  the  air  to  the  desired 
degree,  is  that  of  returning  a  part  of  the  exhaust  air  from  the 
evaporator  to  the  furnace  room  where  it  is  mixed  with  fresh  air, 
reheated  and  passed  over  the  fruit  again.  By  varying  the  propor- 
tion of  the  recirculated  air  any  desired  degree  of  humidity  may  be 
maintained.  As  already  pointed  out,  recirculation  of  a  part  of  the 
air  results  in  a  great  saying  of  fuel. 

By  way  of  summary  it  may  be  stated  that  (1)  evaporation  of 
water  from  a  free  surface  varies  inversely  as  the  relative  humidity, 
(2)  directly  as  the  time,  (3)  directly  as  the  temperature,  and  (4) 
as  the  square  root  of  the  air  velocity.  Dipped  grapes  more  nearly 
approach  a  free  surface  of  water  than  do  most  fruits,  because  of  their 
small  size  and,  therefore,  the  above  relations  will  probably  be  more 
nearly  true  for  grapes  than  for  other  fruits. 

(e)  MISCELLANEOUS  REQUIREMENTS 

In  addition  to  providing  for  the  fundamental  requirements  of 
adequate  heat  supply,  air  circulation  and  control  of  humidity,  the 
evaporator  to  be  thoroughly  satisfactory  should  include  the  following 
features : 

It  should  utilize  its  fuel  efficiently.  This  means  that  the.  transfer 
of  heat  from  the  furnace  to  the  air  should  be  as  complete  as  possible, 
with  very  little  of  the  heat  escaping  through  the  smoke  stack.  It 
also  means  that  radiation  losses  and  losses  through  leaks  should  be 
minimized. 

The  evaporator  should  be  as  convenient^  arranged  as  possible  in 
order  to  reduce  labor  costs  to  a  minimum.  This  is  a  very  important 
point  that  some  manufacturers  have  overlooked.  Frequent  shifting 
of  the  trays  in  some  evaporators  greatly  increases  the  labor  cost:  a 
practice  made  necessary  by  uneven  air  distribution  in  the  evaporator 
and  uneven  drying  of  the  fruit  on  the  trays. 

The  evaporator  should  be  so  arranged  in  relation  to  the  dipper, 
spreading  tables,  sulfur  house,  stemmer,  storage  bins,  etc.,  that  the 
fruit  can  be  handled  efficiently  at  all  points.  This  will  require  careful 
arrangement  of  the  plant. 


428 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


It  is  the  opinion  of  the  writers  that  all  evaporators  representing 
any  considerable  investment  should  be  of  fireproof  construction.  The 
slight  extra  cost  is  an  excellent  investment. 

The  cost  of  an  evaporator  for  grape  drying  must  not  be  excessive 
if  the  investment  is  to  prove  profitable.  On  the  other  hand,  the 
evaporator  should  not  be  of  such  cheap  construction  that  its  period 
of  usefulness  will  be  excessively  short.  At  1919  prices  for  materials, 
it  is  believed  that  a  substantially  constructed  evaporator  similar  in 
design  to  the  University  Farm  Evaporator  described  below  can  be 
erected  and  equipped  for  about  $500  per  fresh  ton  capacity  per  24 
hours. 

IV.      THE    UNIVERSITY    FARM    EVAPORATOR 

This  evaporator  was  constructed  primarily  for  the  purposes  of 
conducting  investigations  in  the  drying  of  grapes  and  other  fruits 
upon  a  commercial  scale  and  to  convert  the  grape  crop  of  the  Univer- 
sity Farm  into  a  marketable  product.  It  was  also  hoped  that  the 
evaporator  would  serve  as  a  model  for  growers  who  might  wish  to 
build  evaporators. 

The  discussion  of  the  evaporator  has  been  taken  up  under  the 
following  topics:  List  of  Materials  and  Cost  of  Construction,  Descrip- 
tion of  the  Evaporator  as  Used  in  1919,  Course  Followed  by  Grapes 
at  Evaporator,  and  Suggested  Revisions  in  Plan  of  University  Farm 
Evaporator. 


(a)   LIST   OF  MATEEIALS  AND   COST   OF   CONSTEUCTION 

The  materials,  labor,  and  equipment  entering  into  the  construction 
of  the  Davis  evaporator  are  given  in  the  following  list : 


Lumber : 

6"  X  6"  rough  redwood  152 

2"  X  6"  S-2E    Oregon   pine 950 

1"  X  6"  pine  sheathing  3500 

2"  X  4"  S-4-S   Oregon  pine 400 

2"  X  4"  rough  pine  for  yard  track 360 

1"  X  4"  T  &  G  flooring 4100 

2"  X  8"  rough  pine  82 

4"  X  6"  rough  pine  88 

4"  X  4"  rough  pine  64 

4"  X  4"  S-4-S  Oregon  pine  for  dipper 8 

3"  X  4"  S-4-S  Oregon  pine  for  dipper 20 

2"  X  3"  S-4-S  Oregon  pine  for  dipper 8 

2"  X  12"  rough  pine  300 

19,000  redwood  shingles 


linear  feet 


$679. 


Bulletin  322  THE  EVAPORATION  OF  GRAPES  429 

2.  Labor:  137%  days  at  $5.00  per  day 687.84 

3.  Plumbing  materials  for  water  and  fuel  supply 28.33 

4.  Electrical  equipment  and  supplies: 

(a)  1  7%  h.p.  3-phase,  110-volt  motor  for  fan $188.80 

(b)  2  transformers,  complete 97.50 

(c)  Wire 117.72 

(d)  2  poles  18.80 

(e)  Switches,   light   sockets,    insulators,    cross    arms,    fuse 

plugs,  etc 25.95 

448.77 

5.  Hardware: 

(a)  Heating   pipe,    12"    riveted:    6    pieces    8'    long,    2 

pieces  1'  long,  2  pieces  20'  long,  6  return  bends,  and 

2   elbows   $135.00 

(b)  2  old  boiler  shells,  6'  X  3' 100.00 

(0)  1  California-Fresno  large  size  gravity  burner 22.50 

(d)  1  Johnson  whirlwind  distillate  burner,  medium  size  ..  85.00 

(e)  1  54"  disc  fan   (American  blower)  182.00 

(/)   1  60"  disc  fan  (American  blower)  239.70 

(g)   1  50-gallon   cauldron   '.'. 25.00 

(h)   2  22"  prune  dipping  baskets 17.00 

(i)    1  set  roller  bearings  for  dipper 17.50 

(j)    250'  iron  T-rail,  8  pounds  per  yard 39.57 

(1c)   3  all  steel  lower  dry-yard  transfer  trucks 56.25 

(1)  13  wooden  frame  dry-yard  trucks 73.13 

(m)   Hinges,  nails,  wire  washers,  furnace  doors,  etc 35.71 

1028.36 

6.  Materials  for  500  trays: 

(a)  Shook:  1000  pieces,  1%"  X  1%"  X  36";  1000  pieces, 
%"  X  iy2"  X  33";  1000  pieces,  %"  X  1%"  X  36"; 
1000  pieces,  %"  X  %"  X  33";  500  pieces,  %"  X  1" 
X  33";  500  pieces,  %"  X  %"  X  34";  1000  pieces, 
1"  X  iy2"  X  36"  for  side  cleats  to  raise  height  of 
trays  $90.00 

(6)   Wire:  1200  linear  feet,  y2"  mesh;  300  linear  feet,  %" 

mesh;   300  linear  feet,  %"  mesh 253.45 

343.45 

7.  Cement,  bricks,  etc.: 

(a)  128  sacks  of  cement $147.34 

(b)  1000  second-hand  brick  (no  charge)  

(c)  400  fire  brick 32.00 

(d)  160  pounds  of  fire  clay 4.80 

(e)  3  loads  of  crushed  rock 6.00 

(/)   4  loads   of  sand 8.00 

(g)   17  loads  of  creek  gravel  (no  charge)  

(h)   1^  barrels  of  lime 4.50 

202.64 

8.  Paint  for  roof  and  stacks 41.75 


430  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

9.  Thermometers: 

(a)   1  recording  thermometer  $52.50 

(&)   2  angle-stem    Fahrenheit    thermometers 39.60 

92.10 

10.  Belting: 

(a)   25'  of  4"  rubber  belting  (estimated)  13.25 

(&)    10'  of  4"  leather  belting,  second  hand   (estimated)  ....       10.00 
(c)   Belt  lacing  25 

23.50 

11.  Miscellaneous  5.91 

Total  $3582.64 

The  cost  of  an  evaporator  of  this  capacity  (6  tons  of  fresh  fruit 
per  charge)  to  the  average  builder  at  1919  prices  for  materials  would 
be  considerably  less  than  the  total  given  above  for  the  following 
reasons.  The  furnace  room  is  twice  as  large  as  necessary  and  the 
outside  walls  were  given  a  special  finish.  One  furnace  and  one  burner 
were  found  to  be  sufficient,  although  for  experimental  purposes  two 
of  each  were  installed.  The  shed  above  the  evaporator  was  built  very 
substantially  of  such  design  and  finish  as  to  compare  favorably  in 
appearance  with  other  buildings  on  the  University  Farm.  A  shed 
less  attractive  in  appearance  but  equally  serviceable  would  probably 
be  built  by  the  average  grower.  One  fan  was  sufficient,  although  for 
experimental  purposes  two  were  installed.  However,  these  fans  were 
of  an  inexpensive  type  and  one  multivane  fan  to  replace  them  would 
cost  as  much  as  the  two  disc  fans  actually  installed.  The  sulfur  house 
was  built  of  cement;  a  wood  sulfur  house  will  answer.  Taking  all 
such  possible  savings  in  cost  into  account  it  is  believed  that  an  evap- 
orator of  the  same  design  and  capacity  as  our  plant  could  be  built 
and  equipped  for  about  $3000,  or  at  a  cost  of  about  $500  per  fresh 
ton  capacity  per  charge. 


(6)   DESCRIPTION    OF    THE    UNIVERSITY   FARM    EVAPORATOR   USED 

IN  1919 

The  evaporator  consists  of  a  tunnel  through  which  the  cars  loaded 
with  fruit  are  moved  during  drying  and  a  fire-proof  furnace  room 
for  heating  the  air  which  is  drawn  or  blown  through  the  tunnel  by 
a  fan.  The  remaining  equipment  is  used  for  preparing  the  fruit  for 
drying  or  for  packing  the  dried  product. 

The  drying  tunnel  and  dipping  outfit  are  housed  beneath  a  shed 
approximately  60  feet  long  and  20  feet  wide.  The  general  appearance 
of  the  complete  plant  may  be  seen  from  the  accompanying  photograph. 


Bulletin  322 


THE    EVAPORATION    OF    GRAPES 


431 


The  tunnel  is  33  feet  long  by  7  feet  high  by  6y2  feet  wide,  inside 
dimensions.  The  walls  and  ceiling  are  constructed  of  1"  X  4"  tongue 
and  groove  pine  on  an  outside  framework  of  2"  X  4"  pine.  The 
floor  is  of  cement  and  slopes  toward  the  furnace  room  to  aid  in  moving 
the  cars  forward.  The  slope  is  14  inch  per  foot ;  for  the  type  of  cars 
used,  this  slope  could  be  considerably  increased  to  advantage. 

The  location  of  the  two  doors  may  be  seen  from  the  accompanying 
sketch.  The  door  openings  are  7  feet  high  by  64  inches  wide  and 
each  is  closed  by  two  tight-fitting  folding  doors.  Transfer  tracks 
enter  each  door  and  connect  with  the  tunnel  track.  The  transfer  track 
rails  are  42  inches  apart  and  are  ordinary  dry-yard  T  rails  of  8  pounds 


Fig.  1. — View  of  the  University  Farm  Evaporator. 


per  yard  weight.  The  tunnel  track  rails  are  set  24  inches  apart  and 
connect  with  the  transfer  tracks  at  each  end  of  the  tunnel. 

An  air  return  flue  1  foot  high  by  6y2  feet  wide  and  33  feet  long 
rests  above  the  drying  tunnel.  This  connects  with  the  tunnel  outlet 
by  a  door  1  foot  by  6y2  feet  which  folds  upward  and  by  a  door  of 
the  same  size  in  the  furnace  room.  The  return  flue  is  constructed 
of  1"  X  4"  tongue  and  groove  over  2"  X  4"  pine.  It  is  used  for 
the  return  of  a  part  of  the  exhaust  air  to  the  furnace  room  where  it 
may  be  mixed  with  fresh  air,  reheated,  and  recirculated. 

The  tunnel  connects  with  the  furnace  room  through  a  60-inch 
disc  fan.  A  54-inch  disc  fan  is  located  at  the  other  end  of  the  tunnel. 
A  7%  h.p.  electric  motor  is  used  to  operate  either  fan.  The  fans  and 
motor  have  pulleys  of  such  size  that  the  60"  fan  is  operated  at  300 
r.p.m.  and  the  54-inch  fan  at  about  350  r.p.m.     When  operated  at 


432  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT    STATION 

the  above  speeds  either  fan  should  deliver  25,000  cubic  feet  of  air 
per  minute  (catalog  rating).  The  two  fans  were  installed  merely 
for  the  purpose  of  comparing  a  blast  fan  with  a  suction  fan. 

The  furnace  room  is  16  feet  long  by  12  feet  wide  by  12  feet  high, 
outside  dimensions.  The  walls  and  roof  are  of  6-inch  reinforced  con- 
crete. Two  old  boiler  shells,  each  6  feet  long  by  3  feet  in  diameter, 
open  at  one  end  for  installation  of  burner,  and  connected  at  the  other 
end  to  a  12-inch  pipe,  have  been  placed  on  opposite  sides  of  the  furnace 
room,  as  shown  in  figure  2.  Each  furnace  is  connected  to  three  lengths 
of  12-inch  heavy  gauge  sheet  iron  pipe  which  is  led  back  and  forth 
above  each  furnace  before  connecting  to  the  smoke  stack  extending 
20  feet  above  the  furnace  room.  The  hot  gases  from  the  furnace 
must  travel  a  distance  of  40  feet  through  the  radiating  pipes  in  the 
furnace  room  before  reaching  the  stack.  One  furnace  is  fitted  with 
a  gravity  burner  and  the  second  with  an  air-blast  burner.  Fuel  is 
supplied  to  the  burners  through  ^-inch  pipes  connected  to  a  110- 
gallon  distillate  drum  placed  on  a  platform  5  feet  above  the  ground. 
In  the  wall  of  the  furnace  room  opposite  the  tunnel  are  located  two 
sets  of  three  doors  each  for  the  admission  of  fresh  air  to  the  furnace 
room  and  tunnel.  One  set  of  doors  is  opposite  each  furnace.  Each 
door  is  about  28  inches  by  20  inches  in  size.  (See  figs.  1  and  2.) 
The  amount  of  air  admitted  to  the  evaporator  is  regulated  by  adjust- 
ing these  doors. 

The  dipping  equipment  is  located  under  the  east  end  of  the 
evaporator  shed.  It  consists  first  of  a  50-gallon  prune-dipping 
cauldron  mounted  over  a  brick  furnace  in  which  is  burned  coal  or 
wood  to  keep  the  lye  solution  in  the  kettle  at  the  boiling  point. 
Adjacent  to  this  kettle  and  at  the  same  height  above  the  floor  (33 
inches)  is  a  cement  vat  of  the  same  size  and  shape  as  the  cauldron. 
This  vat  holds  the  water  used  in  rinsing  the  grapes  after  dipping,  and 
is  equipped  with  a  drain  pipe  and  fresh  water  supply.  The  dipping 
machine  consists  of  the  following  parts.  Two  22-inch  prune-dipping 
baskets  are  hung  at  the  ends  of  3"  X  4"  pieces  which  are  5%  feet 
long  and  pivoted  on  two  4"  X  4"  pieces,  which  in  turn  are  attached 
to  a  6"  X  6"  upright  piece  and  supported  by  2"  X  4"  pieces,  as  shown 
in  figure  2  section.  The  6"  X  6"  upright  pieces  rest  on  a  roller  bear- 
ing pivot.  The  baskets  are  counterbalanced  by  boxes  of  sand.  The 
end  of  each  basket  support  carrying  the  sand  box  is  connected  to  a 
pivoted  handle  so  that  the  basket  may  be  depressed  into  the  lye 
solution  or  rinse  water  by  merely  raising  this  handle.  The  handle 
is  also  used  in  swinging  the  loaded  basket  from  the  loading  chute  to 
the  lye  kettle;  from  lye  kettle  to  the  rinsing  vat,  from  the  rinsing 


Bulletin  322 


THE   EVAPORATION   OP    GRAPES 


433 


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vat  to  the  tray  loading  table,  and  from  this  point  back  to  the  loading 
chute.  This  dipping  machine  is  patterned  closely  after  the  ''Sutter 
County  Merry-Go-Round  Dipper"  used  for  many  years  for  dipping 
Sultanina  grapes  before  drying  and  may  be  purchased  in  complete 
form  from  manufacturers,  although  the  outfit  is  not  complicated  and 
can  be  built  locally.  The  ordinary  prune  dippers  of  various  forms 
may  be  used  successfully,  but  must  be  equipped  for  rinsing  the  dipped 
grapes.     Continuous  dipping  machines  for  grapes  are  available. 


434  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

A  platform.  16'  X  12'  and  2  feet  high  is  placed  outside  the  evapo- 
rator shed  but  adjacent  to  the  dipping  outfit  for  receiving  the  fresh 
grapes.  I  A  concrete  sulfur  house,  7  feet  wide  by  iy2  feet  high  by 
8  feet  long,  inside  measurements,  is  located  a  short  distance  from 
the  shed.  It  is  equipped  with  tight-fitting  folding  doors;  a  6-inch 
adjustable  ventilator  in  roof ;  a  sulfur  pit,  8  inches  deep  and  8"  X  12" 
in  size,  and  tracks  for  drier  cars.    It  will  hold  two  loaded  cars. 

Thirteen  wooden  frame  dry-yard  trucks  were  used.  The  evapo- 
rator held  eight  cars  when  filled  to  capacity  and  each  car  held  42  trays 
of  35  pounds  of  grapes  each,  making  a  total  of  six  tons  of  fresh  grapes 
per  charge.  The  frames  on  the  trucks  were  placed  at  right  angles 
to  the  tracks  upon  which  the  cars  operate.  This  position  of  the  frames 
makes  each  truck  six  feet  wide  and  three  feet  long  and  therefore  only 
one  track  is  necessary  in  the  tunnel.  The  transfer  cars  are  of  steel 
construction  throughout  and  of  the  type  used  in  evaporators  in  Fresno 
County  in  which  raisins  are  dried  for  cap  stemming.  Both  the 
evaporator  and  the  transfer  cars  were  very  satisfactory,  except  for 
the  difficulty  in  moving  the  cars  because  of  the  friction  on  the  axles. 
Roller-bearing  wheels  would  be  much  more  desirable  but  are  costly. 

The  trays  are  three  feet  square.  Each  side  is  constructed  of  one 
piece,  36"  X  1%"  X  1%"  and  one  piece,  33"  X  %"  X  iy2"  J  each  end 
consists  of  one  piece,  36"  X  %"  X  1%"  and  one  piece,  33"  X  %" 
X  %"•  The  tray  is  braced  through  the  center  by  one  piece,  33"  X  %" 
X  1",  and  one  piece,  34"  X  %"  %'•'  Most  of  the  trays  were  made 
with  screen  bottoms  held  between  the  various  pieces  of  shook  listed 
above.  (See  fig.  9.)  The  most  satisfactory  trays  were  of  the  above 
construction  for  the  frame  but  with  narrow  wooden  slats  substituted 
for  the  screen.  Screen  of  14"  mesh  is  much  better  than  that  of  V2" 
mesh.  It  was  found  necessary  to  raise  the  height  of  the  sides  of  the 
trays  by  nailing  to  them  strips  1"  X  IV2"  X  36"  in  size  in  order  to 
give  sufficient  space  for  passage  of  air. 

(c)  COUESE  FOLLOWED  BY  GRAPES  AT  EVAPORATOR 

The  grapes  were  ordinarily  treated  as  follows :  The  fresh  grapes 
were  unloaded  at  the  receiving  platform  and  weighed.  They  were 
then  emptied  into  the  chute  from  which  they  fell  into  the  dipping 
basket.  The  basket  was  immersed  in  the  boiling  lye  solution,  which 
varied  in  strength,  from  y2  per  cent  to  3  per  cent  lye  according  to 
the  variety  of  grapes.  After  5  to  40  seconds'  immersion  in  the  lye 
solution,  the  time  varying  with  the  variety,  the  grapes  were  plunged 
into  cold  water  to  remove  adhering  lye.     The  basket  of  rinsed  grapes 


Bulletin  322 


THE    EVAPORATION    OF    GRAPES 


435 


was  then  transferred  to  an  empty  tray  and  the  grapes  spread  evenly 
by  hand.  The  loaded  trays  were  stacked  in  two  tiers  of  21  trays  each 
on  a  car.  The  loaded  car  was  transferred  to  the  sulfur  house  and 
exposed  to  sulfur  fumes  for  about  30  minutes.  In  some  cases  sul- 
furing  was  omitted.  The  car  of  fruit  then  entered  the  tunnel  at  the 
end  opposite  the  furnace  room  where  the  air  was  moister  and  20  to 
30  degrees  cooler  than  at  the  furnace  end.    As  each  car  of  dried  grapes 


Fig.   3. — Evaporator   car  loaded  with  trays  of  freshly   dipped  grapes, 
transfer  car  beneath  evaporator  car.     Unloading  slat  bottom  tray  at  right. 


Note 


was  removed  through  the  side  door  at  the  furnace  end  of  the  tunnel, 
the  remaining  cars  were  moved  forward  the  length  of  one  car, 
and  a  fresh  car  was  inserted  at  the  exhaust  end.  The  dried  grapes 
were  allowed  to  cool  and  were  then  transferred  to  sacks  for  shipment 
without  stemming. 

All  of  the   above  steps  were  varied  greatly  during  the  various 
experiments. 


436  UNIVERSITY    OP    CALIFORNIA EXPERIMENT    STATION 

(d)   SUGGESTED   EE VISIONS    IN   PLAN   OF   UNIVERSITY    FARM 

EVAPORATOR 

The  evaporator  in  its  first  form  proved  successful.  However, 
the  past  season 's  experience  showed  that  certain  additions  and  changes 
are  desirable  in  order  to  increase  the  efficiency  of  the  plant  and  the 
convenience  of  operation.  The  sketches  shown  in  figures  4  and  5 
indicate  the  construction  of  an  evaporator  recommended  to  growers. 
It  resembles  the  University  Farm  evaporator  very  closely  in  outline 
and  appearance,  but  includes  in  its  construction  the  modifications  and 
additions  noted  below.  Practically  all  of  the  suggested  changes  have 
been  made  and  may  be  seen  by  those  who  wish  to  visit  the  University 
Farm  at  Davis. 

1.  Furnace  Room. — One  furnace,  10'  to  12'  long  by  3'  in  diameter, 
equipped  with  a  medium-size  air-blast  distillate  burner  is  sufficient. 
The  furnace  room  should  be  of  fire-proof  construction,  e.g.,  concrete, 
brick,  or  tile  and  should  be  about  14'  long  by  8'  wide  by  11'  high, 
inside  dimensions.  Attached  to  the  furnace  are  nine  lengths  of  12-inch 
heavy  gauge  black  iron  pipe  distributed  as  shown  in  figure  5,  giving 
a  total  length  of  radiating  pipe,  including  connections,  of  approxi- 
mately 120  feet.  The  pipes  are  arranged  in  three  tiers  of  three  pipes 
each.  The  individual  pieces  are  joined  together  vertically  by  return 
bends  and  horizontally  by  headers  or  T  connections.  A  T  connects 
the  smokestack  to  the  radiating  pipe  system.  This  is  fitted  with  two 
dampers  by  means  of  which  the  gases  of  combustion  may  be  allowed 
to  flow  out  through  the  stack  or  into  the  furnace  room  as  desired. 
This  arrangement  of  pipes  and  clampers  gives  approximately  three 
times  the  heating  surface  furnished  by  the  first  installation  for  one 
furnace  and  also  makes  it  possible  to  use  the  gases  of  combustion 
directly  in  drying. 

At  each  side  of  the  furnace  in  the  end  wall  of  the  furnace  room 
is  situated  an  air  intake  door.  Each  is  one  foot  wide  and  one  and  a 
half  feet  high.  Another  air  intake  door  of  same  size  is  located  two 
feet  above  the  furnace.  All  doors  should  be  sliding  to  enable  regula- 
tion of  air  intake.  (See  revised  plan,  fig.  5.)  The  evaporator  now 
includes  essentially  these  features. 

2.  Connection  of  Furnace  Room  to  Tunnel. — No  fan  to  be  located 
between  the  furnace  room  and  tunnel  and  the  opening  connecting  the 
two  to  be  of  same  size  as  cross  section  of  tunnel ;  that  is,  7  feet  high 
by  6V2  feet  wide. 

3.  Fan, — The  two  disc  fans  of  the  present  installation  to  be 
replaced  by  a  top  vertical  discharge  multivane  fan  with  fan  wheel 


Bulletin  322 


THE    EVAPORATION    OP    GRAPES 


437 


438  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

36  inches  in  diameter  and  connected  to  a  iy2  horsepower  motor  by 
belt  and  pulleys  to  give  about  300  r.p.m.  The  fan  to  be  located  at 
air  exit  end  of  tunnel.  Intake  of  fan  to  be  connected  by  sheet  metal 
housing  to  tunnel  outlet.  The  discharge  of  fan  to  be  connected  to 
return  flue  of  tunnel  and  also  arranged  to  discharge  into  the  open 
air  as  shown  in  figure  5 ;  these  two  connections  to  be  equipped  with 
adjustable  dampers  so  that  any  proportion  of  the  exhaust  air  may 
be  returned  to  the  furnace  room  or  discharged  into  the  open  air. 
This  fan  has  now  been  installed. 

4.  Air  Locks. — During  the  past  season  considerable  heated  air  was 
lost  and  drying  was  interrupted  when  the  doors  of  the  tunnel  were 
opened  to  insert  or  remove  cars,  or  to  enter  the  tunnel  to  take  obser- 
vations on  temperature,  etc.  It  is,  therefore,  very  desirable  to  build 
compartments  at  entrance  and  exit  of  the  tunnel  as  shown  in  figure  4. 
In  using  the  compartment  at  the  entrance  end  of  the  tunnel  the  car 
of  fresh  fruit  enters  the  compartment  through  the  folding  doors  at  the 
side  of  the  compartment.  The  operator  enters  with  the  car  and  closes 
the  doors.  He  then  opens  the  sliding  door  connecting  the  air  lock 
with  the  tunnel,  places  the  car  in  the  tunnel  and  closes  the  sliding 
door.  Finished  cars  are  removed  in  a  similar  manner.  Practically 
no  heated  air  is  lost  or  cold  air  drawn  in  during  the  above  operations. 

The  air  lock  for  entrance  of  fresh  fruit  consists  of  a  compartment 
5%  feet  wide,  7  feet  high,  and  7%  feet  long,  inside  dimensions.  Two 
folding  doors  form  the  side  of  the  air  lock  toward  the  dipping  outfit 
and  a  second  set  of  doors  opens  toward  the  sulfur  house.  The  lock 
for  removal  of  cars  of  dried  fruit  is  of  the  same  dimensions  and  con- 
struction, except  that  it  is  equipped  with  doors  at  the  ends  only. 
Both  locks  are  constructed  of  1"  X  4"  tongue  and  groove  pine  over 
a  frame  of  2"  X  4"  pine.  These  may  now  be  seen  in  place  at  the 
University  Farm. 

5.  Dipping  Tank. — It  was  very  difficult  to  maintain  the  lye  solu- 
tion at  the  boiling  point  during  the  1919  season  because  of  the  small 
size  of  the  dipping  cauldron,  50  gallons,  and  necessity  of  using  wood 
or  coal  instead  of  oil  for  fuel.  The  50-gallon  kettle  has  been  replaced 
by  a  sheet  metal  tank  6'  long  by  3'  wide  by  1%'  deep  mounted  in  a 
fire  brick  furnace  equipped  with  a  medium-size  blast-type  distillate 
burner.  The  above  tank  will  hold  about  200  gallons  of  liquid  and 
presents  a  long  surface  to  the  furnace  flame.  The  experience  of  others 
has  proved  that  a  furnace  and  dipping  tank  of  this  type  can  be 
maintained  at  the  boiling  point  during  continuous  operation. 

6.  Rinsing  Vat. — The  present  50-gallon  rinsing  vat  could  be  in- 
creased to  200  gallons  in  size  to  advantage.     This  would  require  less 


Bulletin  322 


THE    EVAPORATION    OF    GRAPES 


439 


frequent  changing  of  rinse  water.  A  sheet  metal  drain  over  the 
space  between  the  dipping  vat  and  the  rinsing  vat  for  return  to  the 
dipping  vat  of  the  lye  solution  which  drips  from  the  dipping  basket 
would  reduce  the  loss  of  lye  solution. 

7.  Track  System. — The  track  now  located  under  the  shed  at  the 
south  side  of  the  tunnel  will  be  moved  outside  the  shed  and  will 


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Fig.    5. — Sections   showing  fan  connections,   lye   tank,   and   furnace   room,   of 
revised  University  Farm  evaporator. 


connect  to  two  transfer  tracks  as  shown  in  figure  4.  This  track  will 
be  continued  to  the  west  end  of  the  shed  where  it  will  connect  to  a 
transfer  track  which  in  turn  connects  to  the  track  between  the  dipping 
outfit  and  tunnel  entrance.  This  arrangement  will  make  it  possible 
to  move  loaded  and  empty  cars  to  and  from  the  tunnel  without  inter- 
ference. 

8.  Observation  Windows. — Six  or  seven  small  port  holes  about 
one  foot  square  have  been  cut  in  the  north  wall  of  the  tunnel  at  such 
points  that  each  car  of  fruit  in  the  tunnel  may  be  observed  and 
samples  removed.    The  windows  are  closed  by  air-tight  doors. 


440 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


9.  Double  Walls  for  Tunnel. — The  first  tunnel  walls  were  made 
of  one  thickness,  1"  X  4"  T  &  G  over  2"  X  4"  pine  outside  frame. 
The  frame  has  been  covered  with  T  &  G  over  building  paper,  to  make 
the  walls  airtight  and  to  reduce  radiation  losses. 

10.  Tray  Guides  on  Trucks. — Difficulty  was  encountered  during 
the  past  season  in  holding  the  trays  on  the  trucks  in  a  perfectly 
vertical  position.    Upright  guides  of  2"  X  4"  have  been  placed  in  the 


Fig.  6. — Photographs  of  an  evaporator  truck  equipped  with  upright  guide-posts 
for  trays. 


center  of  each  car  frame  and  the  trays  will  be  stacked  against  this 
frame.  The  tunnel  is  wide  enough  to  permit  this  change.  See  figure  6 
which  illustrates  such  a  car  used  in  the  Pearson  evaporator. 

11.  Trays. — Most  of  the  screen  bottom  trays  will  be  converted  into 
slat  bottom  trays  by  replacing  the  screens  with  narrow  wooden  slats 
placed  about  %  of  an  inch  apart.  The  sides  of  all  trays  will  be 
increased  in  height  by  the  addition  of  pieces  36"  X  1"  X  1%"  to 
trays  not  already  so  equipped. 

12.  Air  Baffles. — To  prevent  the  passage  of  heated  air  beneath  the 
cars  during  the  past  season  pieces  of  canvas  were  nailed  to  the  car 
frames.  These  extended  from  the  level  of  the  track  to  the  bottom 
of  the  cars.  These  will  be  replaced  in  part  by  two  enclosed  wooden 
platforms  on  the  tunnel  floor,  one  on  each  side  of  the  tunnel  track, 


Bulletin  322  THe  EVAPORATION  OF  GRAPES  441 

of  such  height  that  the  frames  of  the  trucks  will  barely  clear  them. 
These  platforms  will  be  closed  so  that  the  air  will  not  be  permitted 
to  flow  beneath  the  car  frames  between  the  tracks  and  walls  of  tunnel. 
The  canvas  will  be  retained  on  the  car  frame  between  the  tracks  only. 
It  is  essential  that  all  possible  precautions  be  taken  to  force  the 
air  to  flow  over  the  trays.  Air,  like  water,  follows  the  channels  of 
least  resistance,  and  instead  of  flowing  over  the  trays  tends  to  follow 
all  possible  passages  at  the  sides  of  the  cars,  beneath  the  trucks  or 
above  the  topmost  tray. 

V.     COST  OF  OPERATION 

Because  of  the  fact  that  the  University  Farm  evaporator  during 
the  past  season  was  employed  in  the  drying  of  numerous  small  experi- 
mental lots  of  grapes,  our  cost  of  operation  was  abnormally  high. 
Therefore,  due  allowance  must  be  made  for  this  fact  in  considering 
our  data  on  costs  of  operation  given  in  the  following  summary: 

1.  Total  tons  of  fresh  grapes  handled  at  evaporator 52.18 

2.  Total  tons  of  dry  grapes  handled  at  evaporator 15.65 

3.  Labor  cost  per   fresh   ton $  8.102 

4.  Labor  cost  per    dry    ton $27,015 

5.  Labor  cost  of  dipping  per  dry  ton $  8.78 

6.  Labor  cost  of  unloading  trays  per  dry  ton $10.52 

7.  Labor  cost  of  general  work  per  dry  ton $  5.69 

8.  Labor  cost  of  night  operator  per  dry  ton $     .63 

9.  Cost  of  fuel  per  green  ton  (stove  distillate  at  8c  per  gallon)  $  6.23 

10.  Cost  of  fuel  per  dry  ton  (stove  distillate  at  8c  per  gallon)  $21.52 

11.  Cost  of  electric  light  and  power  per  green  ton  of  grapes $     .50 

12.  Cost  of  electric  light  and  power  per  dry  ton  of  grapes $  1.73 

13.  Containers  for  dried  product  (second-hand  barley  sacks  at  8c  each), 

cost  per  ton  of  dry  grapes $  2.00 

14.  Interest  and  depreciation  at  10%   (on  $3500),  cost  per  green  ton....  $  7.71 

15.  Interest  and  depreciation  at  10%   (on  $3500),  cost  per  dry  ton $22.36 

16.  Total  cost  per   green   ton $28,562 

17.  Total  cost  per   dry   ton $74,620 

18.  Total  cost  per  green  ton,  exclusive  of  depreciation $20,852 

19.  Total  cost  per  dry  ton,  exclusive  of  depreciation $52,260 

If  the  interest  and  depreciation  are  included  in  the  cost  of  opera- 
tion the  total  cost  per  dry  pound  of  grapes  was  in  excess  of  3y2c  and 
per  fresh  pound  over  l^c.  Because  of  our  short  operating  season 
the  item  of  interest  and  depreciation  is  excessively  high.  If  it  is 
omitted  from  the  calculations  the  costs  become  approximately  2%c 
per  dry  pound  and  slightly  over  lc  per  fresh  pound.  It  is  certain 
that  by  conducting  the  University  Farm  evaporating  plant  upon  a 
commercial  basis  and  by  adopting  the  modifications  in  methods  of 


442  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

operation  that  last  season's  experience  have  shown  to  be  desirable, 
the  costs  given  above  could  be  very  materially  reduced. 

IV.       RESULTS    OF   INVESTIGATIONS 

As  many  as  possible  of  the  different  processes  involved  in  the 
drying  of  grapes  in  the  sun  and  in  evaporators  were  investigated.  A 
great  deal  of  information  was  obtained,  although  time  did  not  permit 
the  completion  of  all  the  experiments  undertaken  nor  the  solution 
of  all  of  the  problems  presented.  At  least  one  more  season's  work  is 
necessary  to  obtain  the  data  needed. 

Because  of  the  voluminous  nature  of  the  original  data,  even  when 
condensed  by  tabulation,  it  is  necessary  to  present  the  results  in 
summarized  form.  Investigators  or  others  who  may  be  interested  in 
a  detailed  study  of  our  experimental  results  are  invited  to  inspect 
the  data  filed  in  the  projects  in  our  office. 

The  results  will  be  taken  up  as  nearly  as  possible  in  the  sequence 
in  which  the  various  evaporation  processes  occur. 

(a)  DIPPING 

The  dipping  of  grapes  in  a  hot  lye  solution  before  drying  has 
been  practised  for  many  years  in  the  sun-drying  of  Sultanina  (Thomp- 
son Seedless)  grapes  to  hasten  the  rate  of  drying.  Its  use  in  the 
treatment  of  Muscat  grapes,  table  grapes,  and  many  varieties  of  wine 
grapes  was  thoroughly  tested. 

It  was  found  that  different  varieties  exhibited  a  most  remarkable 
difference  in  their  behavior  in  the  dipping  solution.  Sultanina,  Tokay, 
Emperor,  Zalbalkanski,  Palomino,  Black  Morocco,  and  Cornichon  gave 
excellent  results  when  dipped  in  a  boiling  solution  of  y2  per  cent  to 
1  per  cent  lye  followed  by  rinsing  in  water.  The  skins  of  these  grapes 
were  checked  into  numerous  minute  cracks  extending  from  the  stem 
toward  the  apex  of  the  berries.  Practically  all  berries  on  the  bunch 
responded  to  the  dipping  and  the  checks  were  well  distributed  and 
uniform  in  size.  Solutions  stronger  than  1  per  cent  lye  tended  to 
cause  slipping  of  the  skins  of  some  of  the  berries.  Of  the  grapes  listed 
above,  the  Sultanina  gave  the  best  results,  the  berries  of  this  variety 
requiring  only  3  to  5  seconds'  immersion  in  the  boiling  lye  solution. 
Tokays  required  10  to  15  seconds,  and  the  checks  were  somewhat 
deeper  and  longer  than  those  on  the  Sultanina.  The  same  character- 
istics held  for  the  other  large  varieties  named  above. 

Most  of  the  wine  grape  varieties,  such  as  Petite  Sirah,  Zinfandel, 
Carignane,  Alicante  Bouschet,  St.  Macaire,  Mondeuse,  Crabbe's  Black 


Bulletin  322  THe  EVAPORATION  OF  GRAPES  443 

Burgundy,  Barbera,  Valdepenas,  Refosco,  Lagrain,  Gros  Mansenc, 
Burger,  Franken,  and  Johannesburg  Riesling,  Sauvignon  Vert,  Sau- 
vignon  Blanc,  and  West's  White  Prolific  were  very  difficult  to  check 
by  dipping.  It  was  necessary  with  these  varieties  to  use  a  dipping 
solution  of  2  to  3  per  cent  lye  (17  to  25  pounds  of  granular  sodium 
hydroxid — soda  lye — per  100  gallons  of  water)  and  to  maintain  this 
solution  at  the  boiling  point.  Weak  solutions  had  no  apparent  effect 
except  to  remove  the  bloom.  Many  driers  of  wine  grapes  became 
discouraged  because  of  the  difficulty  in  obtaining  satisfactory  results 
and  dried  their  grapes  without  dipping,  thereby  greatly  increasing 
the  time  necessary  for  drying.  The  secrets  of  success  lie  in  using  a 
lye  dip  of  at  least  2  per  cent  active  lye  and  to  keep  the  solution  actively 
boiling.  Even  under  these  favorable  conditions,  it  was  found  that 
from  20  to  40  seconds'  time  was  necessary  for  the  grape  varieties 
listed  above.  These  varieties  developed  deeper  cracks  than  those 
given  in  the  first  list  above.  The  cracks  were  unevenly  distributed 
and  tended  to  extend  at  right  angles  to  the  vertical  axis  of  the  grapes 
rather  than  parallel  to  that  axis.  Many  berries  became  softened  and 
deeply  cracked  while  others  on  the  same  bunch  exhibited  no  apparent 
effect  of  the  lye.  The  berries  of  some  varieties  tended  to  shatter  badly 
from  the  bunches.  In  spite  of  this  defect,  however,  the  fact  that 
dipping  shortened  the  time  of  drying  by  one  half  was  held  sufficient 
reason  for  dipping. 

Muscat  and  Malaga  grapes,  because  of  their  tough,  thick  skins, 
were  the  most  difficult  grapes  of  all  to  check  by  lye  dipping.  The 
berries  tended  to  burst  before  the  lye  checked  the  skins.  The  cracks 
were  deep  and  unevenly  distributed.  Nevertheless,  dipping  of  these 
varieties  is  necessary  for  rapid  drying.  A  2  to  3  per  cent  solution 
of  lye  at  212°  F.  for  30  to  50  seconds  was  necessary  for  effective 
results. 

It  was  found  practically  impossible  to  check  the  skins  of  eastern 
varieties  such  as  Concord,  Isabella,  etc. 

The  effect  of  dipping  on  the  appearance  of  the  finished  product 
is  very  noticeable.  Dipping  removes  the  natural  bloom  of  the  grapes 
and  imparts  a  glossy  appearance.  Raisins  from  dipped  grapes  are 
more  sticky  than  those  from  undipped  grapes.  The  flavor  is  not 
materially  affected  unless  the  lye  is  not  thoroughly  removed  by  rinsing 
in  clean  water  before  drying.  Where  rinsing  is  not  well  done,  the 
raisins  will  possess  a  distinct  although  not  especially  disagreeable 
"lye"  flavor.  Dipped  grapes  produce  a  raisin  of  sweeter  taste  than 
undipped  because  some  of  the  grape  acid  is  neutralized  by  the  lye. 


444  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT    STATION 

Table  1. — Effect  of  Dipping  on  Eate  of  Evaporation  of  Geapes 

Burger  grapes,  No.  2739  Tokay  grapes,  No.  2737 


Time  in 
hours 

Tempera- 
ture 

Weight  of 
grapes 

undipped, 
grams 

Weight  of 
grapes 
dipped, 
grams 

Time  in 
hours 

Tempera- 
ture 

Weight  of 
grapes 

undipped, 
grams 

Weight  of 
grapes 
dipped, 
grams 

0 

140°  F. 

1500 

1500 

0 

145°  F. 

1200 

1200 

4.5 

140°  F. 

1272 

1038 

2 

145°  F. 

1145 

935 

6 

140°  F. 

1192 

853 

6 

145°  F. 

980 

515 

8 

140°  F. 

1134 

728 

8.5 

145°  F. 

924 

422 

9 

140°  F. 

1082 

633 

10 

145°  F. 

813 

317 

15.5 

140°  F. 

902 

408 

12.5 

145°  F. 

728 

273 

17 

140°  F. 

802 

363 

16.5 

145°  F. 

630 

233 

19.5 

145°  F. 

580 

225 

23.5 

145°  F. 

554 

227 

32 

145°  F. 

518 

220 

38 

145°  F. 

378 

212 

40 

145°  F. 

325 

The  dipping  of  the  fresh  grapes  before  drying  is  remarkable  in 
its  effect  upon  the  rate  of  drying.  Numerous  tests  upon  the  rate  of 
drying  of  dipped  and  undipped  grapes  both  in  the  evaporator  and  in 
the  sun  were  made.  Table  1  and  the  curves  in  figure  7  illustrate  this 
point.  The  data  of  table  1  were  obtained  by  drying  dipped  and 
undipped  grapes  on  small  screen-bottom  trays  in  the  laboratory 
evaporator  at  Berkeley.  This  evaporator  is  so  constructed  that  a 
strong  current  of  heated  air  is  driven  across  the  trays  by  means  of  a 
fan.  Because  of  the  high  velocity  of  the  air,  the  rate  of  drying  was 
rapid.  This  small  evaporator  is  very  useful  for  experimental  purposes 
because  of  the  fact  that  the  temperature  and  humidity  of  the  air  used 
in  drying  may  be  easily  regulated. 

The  results  shown  in  figure  7,  curve  II,  were  obtained  by  weighing 
dipped  and  undipped  lots  of  Carignane  grapes  during  the  drying  of 
these  grapes  on  field  trays  in  the  sun. 

From  the  table  and  curves  it  may  be  seen  that  the  dipped  Tokay 
grapes  were  thoroughly  dried  in  16y2  hours  while  the  undipped  grapes 
of  the  same  variety  were  not  sufficiently  dried  after  40  hours.  Dip- 
ping in  this  case  more  than  doubled  the  speed  of  drying.  Similar 
results  were  obtained  with  Burger  grapes  and  several  other  varieties 
in  laboratory  tests. 

In  the  sun-drying  tests  the  dipped  grapes  lost  65  per  cent  of  their 
weight  and  were  sufficiently  dried  at  20  days,  while  33  days  were 
required  for  the  undipped  grapes  to  reach  the  same  degree  of  dryness. 
Dipping  in  this  case  reduced  the  time  of  drying  by  approximately 
one  third. 


Bulletin  322 


THE   EVAPORATION   OF    GRAPES 


445 


In  addition  to  the  experimental  results  given  above,  measurements 
were  made  to  determine  the  quantity  of  lye  used  in  dipping  different 
varieties  of  grapes.    It  was  found  that  varieties  such  as  Petite  Sirah, 


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Fig.  7. — I,  Curves  illustrating-  effect  of  dipping  on  rate  of  drying  of  Tokay- 
grapes  in  an  evaporator.    II,  Effect  of  dipping  on  rate  of  drying  Carignane  grapes 


Semillon,  and  Zinfandel,  with  tough  skins,  required  about  five  pounds 
of  lye  per  ton  of  fresh  grapes.    Of  this  quantity  about  one  pound  was 


446  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

lost  in  the  rinsing  water  while  the  remaining  four  pounds  represent 
lye  neutralized  by  the  grapes  when  the  grapes  were  immersed  for 
30  seconds  in  the  lye. 

Observations  were  also  made  upon  the  amount  of  lye  lost  in  dip- 
ping Petite  Sirah  grapes  at  the  Pearson  evaporator  at  Yountville. 
The  grapes  were  immersed  in  lye  of  3.2  per  cent  sodium  hydroxid 
for  20  seconds.  After  dipping  2800  pounds  of  grapes  and  adding 
water  to  the  vat  to  replace  that  lost  mechanically  and  by  evaporation, 
it  was  found  that  the  lye  concentration  had  decreased  .6  per  cent. 
This  corresponds  to  a  loss  of  14  pounds  of  lye  per  ton  of  grapes.  Of 
this,  one  sixth,  or  2.3  pounds,  was  neutralized  by  the  grapes  and  the 
remainder,  11.7  pounds,  was  lost  in  the  rinsing  vat.  Based  upon  a 
dipping  period  of  20  seconds,  the  average  amount  of  lye  neutral- 
ized by  such  varieties  as  Petite  Sirah  at  Davis  and  at  the  Pearson 
evaporator  was  approximately  2.5  pounds  per  ton  of  fresh  grapes. 
Theoretically  this  should  reduce  the  acidit}^  of  the  grapes  approxi- 
mately .25  per  cent, 

The  smaller  loss  of  lye  in  rinsing  in  our  tests  was  probably  due  to 
the  fact  that  the  dipped  grapes  were  more  thoroughly  drained  before 
rinsing  and  that  a  stronger  lye  solution  was  used  at  the  Pearson  plant. 
Our  tests  demonstrated  that  the  loss  of  lye  in  rinsing  was  greater  with 
the  stronger  lye  solutions. 

Thin-skinned  varieties,  such  as  the  Sultanina,  required  about  1% 
pounds  of  lye  per  fresh  ton  of  grapes.  Of  this,  about  half  a  pound 
was  lost  in  the  rinse  water  and  1*4  pounds  was  neutralized  by  the 
grapes. 

Grapes  are  coated  with  a  waxy  bloom  which  disappears  in  the  lye 
dip.  It  is  probable  that  this  substance  neutralizes  considerable  quan- 
tities of  the  lye  because  it  is  a  wellknown  fact  that  some  fruit  waxes 
possess  the  power  of  neutralizing  lye. 

It  was  observed  that  shrivelled  over-ripe  grapes  as  well  as  grapes 
that  had  wilted  by  standing  in  boxes  several  days  during  warm 
weather  were  much  more  difficult  if  not  impossible  to  check  in  the  lye 
solution,  thereby  necessitating  a  longer  time  to  dry.  Grapes  that  had 
stood  several  days  in  lug  boxes  and  had  become  moldy  or  had  started 
to  ferment,  softened  and  shattered  badly  from  the  bunches  in  dipping. 
For  these  reasons  grapes  should  be  dipped  as  soon  as  possible  after 
picking. 

A  record  of  the  labor  cost  of  dipping,  spreading  and  stacking  the 
trays  of  grapes  was  kept  for  the  entire  season.  The  following  table 
summarizes  some  of  the  results  obtained. 


Bulletin  322  THE  evaporation  of  grapes  447 

Table  2. — Labor  Eecord  of  Dipping  and  Spreading   Grapes 

Pounds  dipped  per        Labor  cost  per  Labor  cost  per 

Variety  hour  fresh  ton  dry  ton 

Sultanina    2166  $1.49  $5.08 

Tokay 1808  1.79  6.09 

Muscat    1241  2.61  8.19 

Gros  Mansenc 1151  2.81  8.31 

Zinfandel    1073  3.02  10.24 

Petite  Sirah  1005  3.22  10.47 

Average  for  season,  all  varieties $2.62  $8.78 

Because  of  the  fact  that  much  of  the  work  wus  done  with  small 
experimental  lots  the  labor  costs  of  dipping  were  abnormally  high 
and  it  should  be  possible  under  average  commercial  conditions  to 
greatly  reduce  the  costs  given  in  table  2.  The  figures  also  include 
the  cost  of  spreading  the  fruit  and  stacking  the  trays  on  the  drier 
trucks.  Two  men  were  used  in  operating  the  dipper  and  two  in 
spreading  and  stacking  trays.  Therefore,  to  obtain  a  fair  idea  of  the 
labor  cost  of  dipping  only,  the  above  figures  should  be  divided  by  two, 
thus  giving  an  average  labor  cost  of  dipping  for  the  season  of  $1.31 
per  fresh  ton  or  $4.39  per  dry  ton,  or  $0.00214  (%c)  per  dry  pound. 

About  five  to  six  gallons  of  stove  distillate  per  hour  at  6c  to  8c 
per  gallon  was  required  to  maintain  a  tank  containing  approximately 
400  gallons  of  lye  solution  at  the  boiling  point  at  the  Pearson  plant. 
The  total  cost  of  fuel  per  hour  varied  from  30c  to  48c.  This  corre- 
sponds to  a  cost  of  approximately  15c  to  24c  per  fresh  ton  of  Petite 
Sirah  or  similar  grapes. 

(6)   SUN-DRYING  VERSUS  EVAPORATION 

A  very  important  question  before  the  fruit  growers  of  California 
concerns  the  relative  merits  of  drying  fruit  in  the  sun  and  in  evapora- 
tors. Which  of  these  two  methods  will  prove  the  more  profitable  to 
the  growers  depends  upon  several  factors,  the  most  important  of 
which  are:  (1)  relative  yields  of  dry  product,  (2)  quality  of  dry 
product,   (3)  cost  of  drying,   (4)  initial  investment  and  depreciation. 

A  number  of  experiments  were  undertaken  at  Davis  to  compare 
the  yields  of  several  varieties  of  grapes  dried  in  the  sun  with  lots  of 
the  same  varieties  dried  in  the  evaporator.  It  is  to  be  regretted  that 
the  results  were  not  absolutely  conclusive.  The  difference  in  yield  by 
the  two  methods  is  so  small  that  a  large  number  of  tests  will  be  neces- 
sary to  definitely  solve  the  problem.  The  results  of  the  past  season's 
tests  are  summarized  in  the  following  table: 


448  UNIVERSITY    OP    CALIFORNIA EXPERIMENT    STATION 

Table  3. — Summary  of  Results  of  Yields  of  Moisture-Free  Product  per 
100  Pounds  Fresh  Grapes 

By  sun-drying,  By  evaporator, 

pounds  pounds 

Muscat  grapes  25.31  25.93 

Sultanina  grapes  27.79  26.71 

Tokay   grapes   24.10  23.51 

Zinfandel   grapes   35.02  27.59 

Lagrain  grapes  29.88  33.11 

Carignane  grapes  27.42  23.60 

Semillon   grapes 27.93  28,35 

Average,  all  varieties  28.26  25.22 

An  examination  of  the  two  tables  indicates  that  Semillon,  Lag-rain, 
and  Muscat  varieties  gave  higher  yields  in  the  evaporator,  while  the 
Carignane,  Zinfandel,  Tokay,  and  Sultanina  varieties  gave  higher 
yields  by  sun-drying.  Averages  of  all  tests  gave  a  slightly  higher  yield 
for  the  sun-drying  method. 

The  only  conclusion  which  seems  warranted  is  that  our  experiments 
indicate  little  difference  in  the  yields  of  moisture-free  product  obtained 
by  sun-drying  and  evaporation.  If  these  results  are  confirmed  by 
future  tests  it  will  mean  that  the  choice  between  the  two  methods  will 
have  to  be  made  on  relative  quality  of  the  finished  product,  cost  of 
operation,  and  prices  received  for  the  dried  fruit,  rather  than  upon 
comparative  yields. 

The  above  conclusions  are  based  upon  the  relative  yields  of  moist- 
ure-free product.  This  is  obtained  by  means  of  a  calculation  based 
upon  the  drying  ratio  and  moisture  content  of  the  finished  product. 
It  affords  the  only  accurate  basis  of  comparison.  However,  a  compari- 
son of  an  average  of  the  drying  ratios  given  in  table  3  is  of  interest. 
The  average  drying  ratio  for  sun-dried  grapes  was  3.04  as  against  3.21 
for  the  evaporated  grapes,  a  difference  of  .17  or  5.44  per  cent  greater 
yield  in  favor  of  the  sun-drying.  This  would  indicate  that  there  was 
at  Davis  a  tendency  to  dry  the  grapes  in  the  evaporator  to  a  lower 
moisture  content  with  consequent  lower  yield  of  dried  product.  The 
fact  that  the  degree  of  drying  can  be  accurately  regulated  in  the 
evaporator  is  a  strong  point  in  its  favor.  More  will  be  said  about  the 
moisture  content  of  dried  grapes  later. 

White  grapes  dried  in  the  evaporator  were  lighter  in  color  than 
the  same  grapes  dried  in  the  sun  and  to  produce  a  raisin  of  very  light 
color  a  much  shorter  time  of  sulfuring  was  required  for  the  grapes 
dried  in  the  evaporator.  Sultanina  grapes  sulfured  for  a  half  hour 
and  dried  in  the  evaporator  were  as  light  in  color  as  the  same  variety 
sulfured  for  three  hours  and  dried  in  the  sun. 


Bulletin  322  THE  EVAPORATION  OF  GRAPES  449 

Evaporated  grapes  retained  more  of  the  fresh  grape  flavor  and 
developed  much  less  of  a  caramel  or  "raisin"  flavor  than  the  same 
varieties  of  grapes  dried  in  the  sun.  Muscat  grapes  dried  in  the 
evaporator  possessed  a  pronounced  fresh  Muscat  flavor  and  were  more 
acid  or  tart  to  the  taste  than  sun-dried  Muscats.  The  color  and  flavor 
of  sun-dried  Muscat  raisins  has  been  firmly  established  in  the  mind 
of  the  consuming  public  by  extensive  national  advertising.  Therefore, 
although  the  flavor  of  the  Muscat  raisin  made  by  evaporation  more 
nearly  resembles  that  of  the  fresh  fruit,  this  difference  in  flavor  from 
that  of  the  sun-dried  article  makes  it  doubtful  whether  its  merits 
would  be  appreciated  by  the  consumer  unless  it  were  well  advertised. 
Should  over-production  of  Muscat  raisins  ever  occur,  the  drying  of  a 
part  of  the  crop  in  artificial  evaporators  in  order  to  produce  a  raisin 
of  special  quality  might  well  be  considered. 

Red-wine  grapes,  such  as  Zinfandel  and  Petite  Sirah,  dried  in  the 
sun  were  apparently  as  deep  in  color  and  of  as  good  quality  as  the 
same  varieties  dried  in  the  evaporator,  but  when  the  color  and  flavor 
of  the  juices  obtained  by  pressing  the  dried  grapes  after  soaking  in 
water  were  compared  the  juice  from  the  evaporated  grapes  was  deep 
red  in  color  and  of  pleasing  flavor  while  that  from  the  sun-dried  grapes 
was  of  a  brown  color  and  poorer  in  flavor.  These  observations  are 
confirmed  by  tests  made  upon  red-wine  grapes  dried  in  the  sun  at  the 
Kearney  Vineyard  several  years  ago.  It  would  appear  that  sunlight 
injures  the  color  or  that  chemical  changes  taking  place  at  the  low 
temperatures  of  sun  drying  may  cause  oxidation  and  browning  of  the 
color.  If  dried  wine  grapes  are  exported  to  foreign  countries  for  wine 
making  the  evaporated  product  will  be  found  much  superior  to  the 
sun-dried. 

The  relative  costs  of  evaporation  and  sun-drying  have  not  been 
definitely  determined  by  one  season's  operation,  because  the  operation 
of  grape  evaporators  during  the  past  season  was  largely  experimental 
in  nature  and  methods  were  not  standardized.  Our  experience  would 
indicate  that  the  cost  of  evaporating  dipped  grapes  is  no  greater  than 
in  sun-drying  except  for  the  cost  of  fuel  and  power.  The  labor  cost 
is  at  least  no  greater  for  evaporation  and  is  probably  less  than  for 
sun-drying  dipped  grapes.  The  labor  cost  involved  in  drying  grapes 
on  field  trays  in  the  vineyard  is  doubtless  less  than  that  necessary  in 
evaporating,  but  the  higher  quality  and  price  of  evaporated  wine 
grapes  more  than  compensate  for  the  extra  cost  of  evaporation.  This 
fact  was  well  established  during  the  1919  season  when  a  difference  of 
as  much  as  4c  per  pound  existed  in  favor  of  the  evaporated  grapes. 


450  UNIVERSITY    OP    CALIFORNIA EXPERIMENT    STATION 

The  preference  for  the  evaporated  product  is  said  to  be  even  more 
pronounced  at  the  present  time  than  it  was  during  the  past  fall. 

The  fact  that  drying  in  the  sun  incurs  danger  of  loss  by  rain 
damage  is  another  reason  for  favoring  evaporation. 

(c)   SULFURING 

Grapes  of  several  different  varieties  were  sulfured  for  various 
lengths  of  time  and  were  subsequently  dried  in  the  sun  or  in  the 
evaporator.  It  was  found  that  less  than  half  as  long  a  period  of 
exposure  to  sulfur  fumes  was  necessary  for  the  grapes  dried  in  the 
evaporator.  This  is  probably  because  the  period  of  drying  in  the 
evaporator  is  so  much  shorter  than  that  necessary  for  sun-drying  and 
because  the  higher  temperature  of  the  evaporator  reduces  the  tendency 
of  the  fruit  to  darken. 

Red-wine  grapes  which  were  dried  in  the  sun  without  sulfuring 
gave  a  juice  of  brown  color  on  extraction  with  water;  but  the  same 
varieties  of  grapes  which  were  sulfured  for  one  hour  or  longer  before 
drying  in  the  sun  gave  a  water  extract  of  red  color  and  pleasing  flavor. 
Therefore,  it  is  advised  that  red  wine  grapes  that  are  to  be  dried  in 
the  sun  be  sulfured  for  about  one  hour  before  drying. 

It  was  found  that  grapes  dried  in  the  evaporator  or  sun  after  three 
hours'  sulfuring  fermented  readily  when  ground  and  mixed  with 
water;  that  is,  this  amount  of  sulfuring  was  not  sufficient  to  prevent 
the  use  of  such  grapes  for  vinegar  making  in  the  United  States  or 
for  wine  making  when  exported  to  foreign  markets. 

The  color  of  all  grapes  dried  in  the  evaporator  was  improved  by 
a  short  sulfuring.  Thirty  minutes'  exposure  to  sulfur  fumes  was 
sufficient  for  most  white  varieties  and  for  Tokay  and  other  grapes 
of  pink  color.  Fifteen  to  twenty  minutes  improved  the  color  of  red- 
wine  varieties,  although  perfectly  satisfactory  results  are  obtained 
with  such  grapes  without  sulfuring.  Sulfuring  appeared  to  injure 
the  flavor  even  when  used  for  a  very  short  length  of  time,  and  it  is 
doubtful  whether  the  improved  color  compensates  for  the  injury  to 
flavor. 

As  noted  elsewhere  in  this  report,  unprotected  screen  trays  became 
badly  corroded  by  sulfur  fumes  and  the  zinc  salts  so  formed  imparted 
a  metallic  flavor  to  the  fruit.  The  use  of  slat  bottom  trays  would  solve 
this  problem. 

The  results  of  our  Davis  experiments  indicate  that  slightly  greater 
yields  of  dried  product  are  obtained  if  the  grapes  are  sulfured  before 
sun-drying  or  evaporation.    Increased  yields  were  obtained  in  a  large 

- 


Bulletin  322  THE  EVAPORATION  OF  GRAPES  451 

number  of  experiments,  but  were  relatively  small  in  amount.  Further 
tests  must  be  made  to  confirm  the  results  of  the  past  season.  The 
sulfurous  acid  absorbed  by  the  fruit  from  the  burning  sulfur  perhaps 
reduces  loss  by  oxidation  during  drying  and  this  might  account  for 
the  increased  yields  observed.  Further  tests  are  necessary  on  this 
point. 

Sulfuring  is  not  necessary  and  is  not  recommended  as  a  general 
practise  in  drying  wine  grapes. 

(d)   EFFECT  OF  TEMPERATURE  ON  QUALITY  AND  RATE  OF  DRYING 

Theoretically,  the  rate  of  drying  is  directly  proportional  to  the 
temperature,  inversely  proportional  to  the  humidity,  and  proportional 
to  the  square  root  of  the  air  velocity.  These  principles  hold  for  the 
evaporation  of  water  from  a  free  surface. 

Tests  were  first  made  in  the  laboratory  to  determine  the  effect 
of  temperature  on  the  rate  of  drying.  The  air  velocity  and  other 
conditions  were  identical  in  all  cases;  only  the  temperature  being 
varied.  The  following  table  and  curves  give  the  results  of  the  tests 
made  with  Tokay  grapes.  Similar  results  were  obtained  with  Alicante 
Bouschet  grapes. 

Table  4. — Effect  of  Temperature  on  Rate  of  Drying  of  Tokay  Grapes 


140°  ] 

h\-145°  F. 

160°  F. 

-165°  F. 

190°  F, 

-200°  F. 

Time  in 
hours 

Weight  in 
grams 

Time  in 
hours 

Weight  in 
grams 

Time  in 
hours 

Weight  in 
grams 

0 

2000 

0 

2000 

0 

2000 

6 

980 

4 

1100 

3 

850 

10 

585 

9 

605 

5.5 

565 

16 

520 

14 

440 

7.5 

485 

20 

500 

25 

498 

29 

480 

In  large-scale  experiments  made  by  one  of  the  authors*  dipped 
Alicante  Bouschet  grapes  were  dried  in  six  hours  at  190°  F.,  whereas 
sixteen  hours'  time  was  required  to  dry  the  same  variety  of  grapes 
at  160°  F. 

The  grapes  dried  at  190°  F.  in  the  large-scale  tests  at  Yountville 
were  dried  in  recirculated  air  of  relatively  high  humidity.  They 
appeared  to  be  of  equal  quality  in  all  respects  to  the  grapes  of  the 
same  variety  evaporated  at  160°  F.     Alicante  Bouschet  grapes  dried 


*  A.  W.  Christie,  in  cooperation  with  J.  W.  Pearson  and  G.  B.  Ridley  in  the 
Pearson  evaporator  at  Yountville. 


452 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


in  the  small  laboratory  evaporator  at  190°  F.  appeared  to  be  of  equal 
quality  to  those  dried  at  145°  F.  and  165°  F.,  although  when  the  grapes 
were  left  in  the  evaporator  for  several  hours  at  190°  F.  to  200°  F. 
after  becoming  dry,  a  noticeable  caramelized  flavor  developed.  Tokay 
grapes  developed  the  caramelized  flavor  more  rapidly  than  did  the 
Alicante  Bouschet  and  exhibited  this  flavor  to  an  appreciable  degree 
even  when  removed  from  the  evaporator  as  soon  as  sufficiently  dry. 
The  tests  indicate,  however,  that  temperatures  of  190°  F.  to  200°  F. 
under  certain  conditions  may  be  safely  used  for  Alicante  Bouschet 
grapes  and  probably  for  other  red-wine  grapes.  Recent  analyses  of 
the  above  lots  of  dried  grapes  show  that  a  great  deal  of  sugar  was 
lost  by  action  of  heat  at  190°  F. 


I 


ZJA^rZCT    Or    T^MPLR/iTi/RE 


I 


Qrt   F?A  rr     OIL ntW/rvG 


e  3  /o         /%,       /+         '6/8        Ao 

Fig.  8. — Curves  illustrating  the  comparative  rates  of  drying  of  Tokay  grapes 
at  three  different  temperatures. 


(e)  EFFECT  OF  CONSTEUCTION  OF  TEAYS 

Most  of  the  trays  used  in  our  experiments  consisted  of  a  wooden 
frame,  3'  X  3',  with  a  wire-screen  bottom.  Screens  of  y2,  %  and  ^ 
inch  mesh  were  used.  In  addition  to  the  screen-bottom  trays  a  few 
trays  were  constructed  with  slat  bottoms.  The  slats  were  about  y2 
by  %  inch  in  size  and  were  placed  about  %  of  an  inch  apart.  The 
accompanying  figure  illustrates  the  construction  of  these  trays. 

The  framework  of  each  tray  consisted  of: 

2  pieces,  36"  X  1%"  X  1%";         2  pieces,  33"  X  %"  X  %"; 

2  pieces,  36"  X  %"  X  1%";  1  piece,  33"  X  %"  X  1";   and 

2  pieces,  33"  X  %"  X  1%";  1  piece,  34"  X  %"  X  %"• 


Bulletin  322 


THE    EVAPORATION    OF    GRAPES 


453 


The  36"  X  1%"  X  1%"  pieces  over  pieces  33"  X  %"  X  iy2" 
formed  the  sides  of  the  trays.  These  trays  are  the  standard  trays  used 
at  Fresno  for  drying  raisins  preliminary  to  cap  stemming.  It  was 
found  that  the  trays  were  not  deep  enough  for  grape  varieties  pro- 
ducing large  bunches.  Therefore,  strips  %"  X  l1/^"  were  nailed  to 
the  side  strips  to  increase  the  height  of  the  sides  of  each  tray  suf- 
ficiently for  the  bottoms  of  the  trays  to  clear  the  bunches  of  grapes  on 
the  tray  beneath.  This  gives  a  distance  of  3  inches  between  screens, 
a  space  sufficient  to  permit  free  circulation  of  air  and  rapid  and  even 
drying. 


Fig.  9. — Photographs  of  screen  bottom  and  slat  bottom  trays  used  in  experi- 
ments at  Davis.     Trays  are  3'  X3'  in  size. 


Several  serious  objections  to  screen  trays  were  encountered.  The 
most  serious  was  the  tenacity  with  which  the  dried  grapes  adhered  to 
the  screen.  The  time  of  two  or  three  men  was  needed  to  scrape  the 
dried  grapes  from  the  trays  whenever  the  evaporator  was  operated  to 
full  capacity.  Users  of  other  evaporators  experienced  the  same  dif- 
ficulty, except  where  the  grapes  were  dried  without  dipping.  The 
juice  from  dipped  grapes  dried  to  a  thick  syrup  at  the  point  of  contact 
of  the  berries  and  screen,  thus  cementing  the  fruit  firmly  to  the  trays. 
The  vigorous  scraping  necessary  to  remove  the  fruit  was  severe  on 
the  wire  screens  and  wooden  frames  of  the  trays;  many  of  the  trays 
became  more  or  less  weakened  in  one  season's  use  on  this  account. 

Where  the  grapes  were  sulfured  the  sulfurous  acid  generated  by 
the  burning  sulfur  attacked  the  zinc  coating  of  the  wire  screens  to 
such  an  extent  that  soluble  zinc  salts  were  formed  in  sufficient  quantity 
to  impart  a  metallic  taste  to  the  fruit. 


454  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Paraffine  was  tested  as  a  coating  for  the  trays.  It  was  melted  and 
applied  to  the  screens  with  a  brush.  It  protected  the  screen  fairly 
well  against  corrosion,  but  caused  the  dried  fruit  to  adhere  to  the 
screen  even  more  tightly  than  where  no  paraffine  was  used.  Asphalt 
and  Gilsonite  base  paints  and  other  special  paints  and  varnishes  either 
became  soft  and  adhered  to  the  fruit  in  the  evaporator  or  became 
brittle  and  chipped  off  the  screen  during  removal  of  the  dried  fruit 
from  the  trays.  The  authors  are  still  searching  for  a  suitable  tray 
coating  and  have  obtained  several  promising  materials. 

The  rates  of  drying  for  grapes  of  several  varieties  on  screen  and 
on  slat-bottom  trays  were  compared  by  placing  grapes  on  slat-bottom 
trays  on  cars  loaded  with  screen  trays  containing  the  same  variety  of 
grapes.  No  difference  in  the  rates  of  drying  could  be  noticed.  It 
was  found,  however,  that  the  dried  grapes  were  removed  with  great 
ease  from  the  slat-bottom  trays,  there  being  practically  no  tendency 
to  stick.  Furthermore,  these  trays  are  rigid  and  retain  their  shape 
without  sagging.  There  is,  of  course,  no  formation  of  metallic  salts 
or  corrosion  of  the  trays  by  the  action  of  sulfur  fumes.  Slat-bottom 
trays  may  be  constructed  at  less  cost  than  screen  trays. 

Trays  with  solid  wooden  bottoms  of  the  type  ordinarily  used  in 
sun-drying  were  compared  with  screen-bottom  trays  to  determine  the 
relative  rates  of  drying  on  each.  This  is  an  important  point  because 
many  grape  growers  already  possess  ordinary  field  trays  and  naturally 
wish  to  make  use  of  them  if  they  construct  an  evaporator.  A  test  was 
first  made  in  a  commercial  evaporator  in  which  the  air-blast  rises 
vertically  from  a  fan.  In  this  evaporator  the  fruit  (apricots)  dried 
only  one  half  as  rapidly  on  the  solid  wooden  bottom  trays  as  on  the 
screen  trays.  In  our  small  laboratory  evaporator,  however,  the  tests 
were  repeated  with  grapes  and  the  use  of  a  horizontal  blast  of  air; 
that  is,  the  heated  air  was  blown  across  the  trays.  Five  different 
varieties  of  grapes  were  tested.  The  different  trays  were  of  exactly 
the  same  length,  breadth  and  depth,  the  only  difference  being  in  the 
construction  of  the  tray  bottoms. 

The  rate  of  drying  in  the  case  of  the  Muscat  and  Tokay  grapes 
was  practically  a^  rapid  on  the  wooden  trays  as  on  the  screen  trays. 
Burger  grapes  dried  somewhat  more  rapidly  on  screen  than  on  wood, 
although  the  difference  was  not  very  pronounced.  This  indicates  that 
the  ordinary  solid  bottom  sun-drying  trays  can  be  successfully  used 
in  an  evaporator  where  a  horizontal  air  blast  is  employed  providing 
the  trays  are  separated  by  blocks  or  cleats  to  permit  an  ample  flow 
of  air. 


Bulletin  322 


THE    EVAPORATION    OF    GRAPES 


455 


(/)   COMPARISON  OF   GRAVITY   AND   AIR-BLAST  BURNERS 

Two  furnaces,  each  consisting  of  an  old  boiler  shell  6  feet  long 
by  3  feet  in  diameter  connected  to  approximately  40  feet  of  12-inch 
pipe  were  installed  in  the  furnace  room  of  the  evaporator  at  Davis. 
In  one  of  these  was  placed  a  medium-size  air-blast  burner  and  in  the 
second  furnace  a  large-size  gravity  burner.  Except  in  very  cold 
weather,  it  was  found  possible  to  maintain  the  air  entering  the  evapo- 
rator at  140°  F.  to  145°  F.,  using  either  burner  alone.     When  the 


:ffiL 


SECT/ ON      Or  UNIVERSITY  RfiRM     DIRROR 
Fig.  10. — Sketch  of  dipping-  machine  used  at  University  Farm  evaporator,  1919. 

exhaust  air  was  allowed  to  escape  freely  from  the  tunnel  outlet, 
practically  the  full  capacity  of  one  burner  was  required  to  maintain 
the  evaporator  above  140°  F.,  but  when  a  large  portion  of  the  air 
was  recirculated  it  was  possible  to  maintain  this  temperature  by  using 
the  air-blast  burner  at  one  half  to  two  thirds  capacity. 

The  air-blast  burner  was  somewhat  more  efficient  than  the  gravity 
burner  for  the  reason  that  the  latter  gave  incomplete  combustion  of 
the  fuel.  This  fact  was  indicated  by  the  black  smoke  which  issued 
from  the  stack  of  the  gravity  burner  furnace  and  by  the  large  accumu- 
lation of  soot  in  the  radiating  pipes.  It  was  found  necessary  to  seal 
the  joints  of  the  radiating  pipes  of  this  furnace  with  fire  cement  to 
prevent  the  soot  from  entering  the  tunnel  with  the  heated  air  and 
causing  blackening  of  the  fruit.     The  air-blast  burner  on  the  other 


456  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

hand  produced  no  soot;  in  fact,  it  was  found  possible  to  pass  all  the 
products  of  combustion  of  this  furnace  through  the  drying  tunnel 
without  injury  to  the  grapes. 

The  gravity  burner  tended  to  heat  the  furnace  walls  less  uniformly 
than  did  the  air-blast  burner.  The  flame  of  the  latter  extended 
throughout  the  entire  length  of  the  furnace,  whereas  that  of  the 
gravity  burner  was  more  localized  and  most  intense  immediately 
above  the  burner.  An  air-blast  burner  has  another  advantage  in  that 
a  full  flame  is  obtained  immediately  on  lighting  the  burner,  whereas 
at  least  a  half  hour  is  required  to  bring  the  gravity  burner  to  full 
capacity. 

In  spite  of  these  defects  the  gravity  burner  was  found  to  be  fairly 
satisfactory.  It  could  be  used  successfully  in  localities  where  electric 
power  is  not  available  for  the  operation  of  an  air-blast  burner.  It  is 
cheap,  easily  installed,  and  simple  in  operation. 

Our  results  demonstrated  that  one  blast  burner  is  sufficient  for  an 
evaporator  of  this  size  provided  a  large  proportion  of  the  air  is  recir- 
culated. The  furnaces  were  only  six  feet  in  length.  One  furnace 
ten  or  twelve  feet  long  would  be  much  more  satisfactory  because  the 
flame  of  the  air-blast  burner  often  extended  beyond  the  furnace  into 
the  radiating  pipes.  Only  40  feet  of  radiating  pipe  was  used  on  each 
furnace.  At  least  twice  this  amount  should  have  been  installed  in 
order  to  reduce  stack  losses  of  heat  to  a  minimum.  By  constructing 
the  furnace  according  to  these  suggestions  and  eliminating  one  furnace 
it  would  be  possible  to  greatly  reduce  the  size  and  cost  of  the  air- 
heating  room.     (See  revised  plans  for  further  details.) 

(g)   OOMPAKISON  OF  DISC  AND  MULTIVANE  FANS 

No  direct  comparison  of  these  two  types  of  fans  was  made,  but  the 
rate  of  air  flow  through  a  large  tunnel  equipped  with  the  multivane 
type  of  fan  was  determined  and  compared  with  the  results  of  similar 
readings  made  upon  the  University  Farm  evaporator  which  was 
equipped  with  a  disc  fan. 

Our  drying  tunnel  was  approximately  33  feet  long  and  6V2  X  7 
feet  in  cross  section.  The  rate  of  air  flow  over  the  trays  on  the  last 
car  when  the  tunnel  was  filled  with  loaded  cars  varied  from  100  to 
350  feet  per  minute.  The  average  was  approximately  220  feet  per 
minute. 

The  drying  tunnel  of  an  evaporator  in  Napa  County  which  was 
used  for  comparison  was  approximately  68  feet  long  and  of  about 
the  same  cross  section  as  our  evaporator.    In  this  evaporator  a  multi- 


Bulletin  322 


THE    EVAPORATION    OP    GRAPES 


457 


vane  fan  was  operated  at  such  speed  as  to  deliver  18,000  cubic  feet 
per  minute  (catalog  rating),  actual  delivery  12,500  cubic  feet  per 
minute  with  loaded  tunnel.  (The  disc  fan  was  rated  at  25,000  cubic 
feet  per  mnute.)  When  approximately  60  feet  of  the  larger  drying 
tunnel's  length  was  filled  with  loaded  cars  the  rate  of  air  flow  over 
the  trays  on  the  last  car  was  approximately  420  feet  per  minute.  The 
multivane  fan  operated  against  approximately  double  the  resistance 
of  the  disc  fan  because  the  loaded  tunnel  was  twice  as  long.  In  spite 
of  this  greater  resistance  the  multivane  fan  gave  a  much  greater  rate 
of  air  flow ;  a  fact  which  accounts  for  the  more  rapid  rate  of  drying 
in  this  evaporator. 


Fig.  11. — Multivane  fan  on  left;  disc  fan  on  right. 


These  observations  were  not  extensive,  but  nevertheless  clearly 
indicate  the  great  superiority  of  the  multivane  fan  over  the  disc 
fan.  The  former  is  considerably  more  expensive  than  the  latter  but 
the  difference  in  price  is  more  than  compensated  for  by  the  advantages 
of  the  multivane  type.  In  addition  to  causing  more  rapid  drying,  it 
permits  the  use  of  longer  tunnels,  and  thus  makes  possible  a  more 
complete  utilization  of  the  moisture-absorbing  power  of  the  air. 

It  is  our  opinion  that  the  ideal  ventilating  system  for  an  evaporator 
would  be  a  multivane  exhaust  fan  so  arranged  in  relation  to  the  air- 
heating  system  and  air-return  flue  that  the  heated  air  may  be  drawn 
by  the  fan  over  the  trays  by  suction,  and  any  desired  proportion  of 
this  exhaust  air  returned  to  the  furnace  room  to  be  mixed  with  fresh 
air  and  recirculated. 


458  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

This  would  combine  the  advantages  of  recirculation  and  humidity 
control  with  that  of  an  exhaust  fan  of  the  multivane  type. 

The  planing  mill  exhaust-type  of  fan,  which  is  a  more  powerful 
type  than  the  multivane,  has  been  used  successfully  by  a  commercial 
evaporating  company.  This  type  of  fan  requires  for  operation  con- 
siderably more  power  than  the  multivane  fan  of  the  same  rating.  It 
remains  to  be  seen  whether  the  planing  mill  exhauster  will  demonstrate 
advantages  which  will  compensate  for  this  greater  cost  for  power. 

(ft)   EXHAUST  VERSUS  POSITIVE  BLAST  FAN 

The  evaporator  at  Davis  was  equipped  with  a  60-inch  disc  fan 
at  the  furnace  end  of  the  tunnel.  This  was  connected  to  a  7%  h.p. 
electric  motor  and  was  operated  at  such  speed  as  to  deliver  theo- 
retically 25,000  cubic  feet  of  air  per  minute  (catalog  rating).  At  the 
outlet  end  of  the  tunnel  was  located  a  54-inch  disc  fan,  which  could 
be  used  as  a  suction  or  exhaust  fan  at  such  speed  that  25,000  cubic 
feet  of  air  per  minute  should  theoretically  (catalog  rating)  have  been 
drawn  through  the  tunnel.  As  a  matter  of  fact  the  actual  amount  of 
air  delivered  varied  from  about  10,000  cubic  feet  to  15,000  cubic  feet 
per  minute  with  each  fan. 

The  evaporator  was  operated  experimentally  for  a  period  of  sev- 
eral days  with  the  suction  fan  or  the  blast  fan  only.  The  conditions 
in  the  experiments  being  similar  in  other  respects,  the  rate  of  drying 
of  Tokay  grapes  was  used  as  a  basis  for  comparison.  The  following 
table  summarizes  the  more  important  results  obtained. 

Table  5. — Comparison  of  Suction  and  Positive  Blast  Fans 


1.  Fuel  consumption,  gallons  per  hour  .... 

2.  Average  temperature  of  air  at  furnace 

end  of  tunnel 

3.  Average  temperature  of  outside  air  .... 

4.  Average  increase  of  temperature 

5.  Humidity  at  furnace  end  of  tunnel  .... 

6.  Time  to  dry  tokay  grapes,  hours 

7.  Average  rate  of  air  flow  at  end  of  tun- 

nel,  feet   per   minute 180  198 

8.  Eelative   efficiency   based   on   time   of 

drying  and  fuel  consumption,  test 

II   taken   as    100 60.22%  100% 


•sitive  blast  fan 

I 

Suction  fan 
II 

7.50 

8.8 

133.4°  F. 

138.02°  F. 

67.7°  F. 

67.3°  F. 

65.7°  F. 

70.72°  F. 

3% 

7% 

73 

37.5 

Bulletin  322  TIIE  EVAPORATION  OF  GRAPES  459 

The  data  given  in  the  above  table  indicate  that  the  suction  fan  is 
much  more  satisfactory  and  efficient  than  the  positive  blast  fan.  The 
slightly  higher  temperature  of  the  air  and  the  slightly  greater  rate 
of  air  flow  probably  accounts  for  the  more  rapid  rate  of  drying  with 
the  suction  fan. 

In  addition  to  more  rapid  drying,  the  suction  fan  appeared  to 
cause  the  grapes  to  dry  more  evenly.  However,  too  few  observations 
were  made  upon  this  point  to  determine  conclusively  whether  the 
difference  was  appreciable. 

From  the  results  of  the  above  tests  it  would  appear  that  evapora- 
tors equipped  with  the  disc  type  of  fan  should  make  use  of  this  fan 
as  a  suction  fan  rather  than  as  a  positive  blower.  It  can  not  be  stated 
whether  the  same  relation  holds  true  for  other  types  of  fans  such  as 
the  multivane  and  mill  exhaust  fans. 

(i)  EECIRCTJLATION  OF  AIE 

The  evaporator  was  of  such  construction  that  any  proportion  of 
the  air,  after  its  passage  through  the  tunnel,  could  be  returned  to 
the  furnace  room  to  be  reheated  and  recirculated.  A  description  of 
the  recirculation  system  will  be  found  in  the  plans  and  specifications. 

In  order  to  determine  the  relative  rates  of  drying  and  relative  fuel 
efficiency  three  tests  were  made.  In  one  of  these  tests,  the  positive 
blast  fan  was  used  with  outlet  of  tunnel  completely  opened  and  return 
air  flue  closed  so  that  none  of  the  air  was  recirculated.  In  another 
test,  the  tunnel  outlet  was  closed  to  such  a  point  that  the  air  outlet 
was  approximately  three  inches  wide  and  seven  feet  long.  The  return 
air  flue  was  opened  as  completely  as  possible,  permitting  a  large  pro- 
portion of  the  air  (approximately  75%)  to  recirculate.  In  the  third 
test,  both  the  tunnel  outlet  and  the  return  flue  were  left  completely 
open.  This  permitted  the  recirculation  of  a  smaller  proportion  of 
the  air  than  in  the  second  test.  A  great  many  observations  on  the 
rate  of  air  flow,  humidity,  and  rates  of  drying  were  made,  but  only 
the  more  essential  results  are  given  in  table  6  on  page  460. 

In  addition  to  the  data  given  on  rates  of  drying,  it  may  be  stated 
that  Carignane  grapes  were  dried  in  the  first  test  in  20  hours  and  the 
maximum  time  required  for  any  variety  in  this  test  was  33  hours.  In 
the  second  test,  the  minimum  time  of  drying  was  46  hours  and  the 
maximum  73  hours;  while  in  the  third,  58  and  68  hours'  time,  respec- 
tively, were  required. 

Of  the  conditions  existing  in  the  evaporator  during  these  three 
tests  the  temperature  variation  was  the  factor  which  would  affect  the 


460  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

rates  of  drying  to  the  greatest  degree.  The  fact  that  it  was  possible 
to  maintain  a  higher  temperature  with  the  same  fuel  consumption 
during  recirculation  accounts  for  the  greater  efficiency  of  this  method. 
The  figures  would  indicate  that  the  saving  in  fuel  by  use  of  recircu- 
lation was  approximately  41%,  basing  this  calculation  upon  a  com- 
parison of  the  first  and  second  tests. 

Table  6. — Effect  of  Recirculation  on  Fuel  Efficiency  and  Eate  of  Drying 

Recirculation,  No  Recirculation. 

Tunnel  outlet  recirculation.  Tunnel  outlet 

nearly  closed.  Blast  fan.  completely  open. 

Observation                                           I  II  III 

1.  Average     fuel     consumption 

per  hour,  gallons 7.57  7.50  6 

2.  Average  temperature  of  air 

at  furnace  end  of  tunnel       141.1°  F.  133.4°  F.  127.4°  F. 

3.  Average  temperature  of  out- 

side air  65.5°  F.  67.7°  F.  71.1°  F. 

4.  Average     increase     in     tem- 

perature of  air 75.6°  F.  65.7°  F.  56.3°  F. 

5.  Volume      of      air      passing 

through  tunnel,  cubic  feet 
per  minute  (approxi- 
mate)      12,800  12,800  12,800 

6.  Humidity  of  air  at  furnace 

end  of  tunnel 10%  3%  7% 

7.  Average  time  required  to  dry 

grapes  of  same  lot,  hours        27.5  47  58.6 

8.  Fuel  required  to  dry  six  tons 

of  grapes,  gallons 208  352  351 

9.  Relative  efficiency  based  on 

time  of  drying  and  fuel 
consumption  (test  I 
taken    as    100)  3  00%  59.14%  59.30% 

Small-scale  tests  in  the  laboratory  evaporator  confirmed  these 
observations.  It  was  found  that  the  burning  of  only  about  one  half 
as  much  gas  was  necessary  to  maintain  a  given  temperature  when 
most  of  the  air  was  recirculated.  In  these  experiments  it  was  prac- 
tically impossible  to  over-dry  grapes  when  most  of  the  air  was  re- 
circulated. The  grapes  dried  to  a  certain  moisture  content  and 
remained  at  that  degree  of  dryness  even  when  the  evaporator  was 
operated  for  a  number  of  hours  after  this  condition  was  reached. 
This  indicates  that  it  is  possible  to  control  the  moisture  content  of 
the  finished  product  by  accurate  control  of  the  proportion  of  recircu- 
lated air.  The  importance  of  this  fact  can  not  be  overemphasized, 
because  it  is  very  difficult  to  judge  by  observation  of  the  grapes  in 
the  evaporator,  whether  they  are  sufficiently  dry.  The  tendency  of 
the  beginner  is  to  over-dry,  which  results  in  a  low  yield  of  inferior 
fruit. 


Bulletin  322  THe  EVAPORATION  OP  GRAPES  461 

These  results  were  further  confirmed  by  experiments  made  with  a 
large  commercial  evaporator  at  Yountville.*  Similar  observations 
have  been  made  by  T.  I.  Casey  and  other  manufacturers  and  users 
of  evaporators  equipped  with  the  recirculation  system. 

A  third  advantage  of  recirculation  claimed  by  Mr.  Paul  F.  Nichols 
of  the  United  States  Department  of  Agriculture  is  that  higher  tem- 
peratures of  drying  may  be  used  without  injury  to  the  fruit,  if 
recirculation  of  the  air  is  employed.  Our  own  preliminary  experi- 
ments indicate  this  to  be  true,  but  our  investigations  on  this  point  have 
not  been  extensive  enough  to  warrant  definite  conclusions. 

We  wish,  therefore,  to  repeat  a  statement  made  earlier  in  this  pub- 
lication, viz.,  that  the  prospective  purchaser  or  builder  make  certain 
that  the  evaporator  shall  be  so  constructed  that  any  proportion  of 
the  air  used  in  drying  may  be  recirculated. 

(j)   DIRECT  USE  OF  GASES  OF  COMBUSTION  IN  DRYING 

In  most  evaporators  a  large  amount  of  heat  is  lost  in  the  gases 
leaving  the  smoke  stack.  It  is  evident  that  this  loss  could  be  elimin- 
ated if  these  gases  may  be  passed  through  the  evaporator  after  mixing 
with  a  sufficient  quantity  of  outside  air  to  give  the  desired  tempera- 
ture. This  method  has  been  used  for  many  years  in  the  drying  of 
garbage  and  more  recently  in  drying  kelp  (sea  weed).  Until  recently, 
it  had  not  been  applied  to  the  drying  of  fruits,  because  of  the  difficulty 
in  eliminating  all  soot,  smoke,  and  disagreeable  odors  in  the  burning 
of  the  fuels  heretofore  in  use.  It  has  been  found  during  the  past  two 
or  three  years,  however,  that  the  products  of  combustion  of  natural 
gas  may  be  used  directly  in  the  drying  of  fruits  without  injury  to 
the  quality  of  the  dried  product.  At  least  three  different  types  of 
evaporators  are  now  successfully  using  this  fuel  in  the  above  way. 

More  recently,  improvements  in  the  design  of  air-blast  burners 
using  stove  distillate,  have  made  possible  such  complete  combustion 
of  this  fuel  that  the  gases  of  combustion  do  not  affect  the  flavor,  odor, 
or  color  of  the  fruit.  In  one  evaporator,  in  which  this  method  has 
been  highly  developed,  the  fuel  is  burned  in  a  long  arched  firebrick 
furnace  in  which  is  used  a  special  form  of  air-blast  burner.  The 
furnace  opens  directly  into  the  flue  leading  to  the  fan.  This  flue  is 
fitted  with  a  cold-air  intake.  By  regulation  of  the  size  of  this  intake 
the  mixed  air  and  gases  of  combustion  are  given  the  desired  tempera- 
ture before  they  reach  the  fan.     The  furnace  gases  may  during  the 


*  These  tests  were  made  in  the  Pearson  evaporator  in  cooperation  with  Messrs. 
Pearson  and  Ridley. 


462  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

time  necessary  to  heat  the  furnace  be  diverted  into  a  smoke  stack. 
This  is  necessary  because  a  cold  furnace  prevents  complete  combustion. 

It  was  found  that  grapes  and.  apples  could  be  dried  in  this  type 
of  evaporator  without  injury  to  quality  from  soot  or  fumes.  The 
efficiency  of  this  method  in  heating  air  is  remarkable,  tests  showing 
that  over  98%  of  the  heat  liberated  in  the  combustion  of  the  fuel  was 
applied  in  heating  the  air.* 

The  furnace  at  the  University  Farm  was  not  designed  for  the 
direct  use  of  the  gases  of  combustion,  but  in  order  to  obtain  a  rough 
comparison  of  the  relative  efficiency  of  direct  and  indirect  heating 
of  the  air,  the  furnace  equipped  with  the  air-blast  burner  was  so 
arranged  as  to  permit  the  gases  of  combustion  to  escape  into  the 
furnace  room  and  to  be  drawn  through  the  evaporator  by  a  suction 
fan. 

Tokay  grapes  were  dried  in  20  hours.  The  quality  of  the  dried 
product  was  equal  to  that  of  the  product  dried  by  air  heated  in  the 
usual  way.  A  comparison  of  the  temperatures  attained,  volume  of  air 
heated  and  fuel  consumption  in  the  two  methods  are  shown  in  the 
following  table. 

Table  7. — Effect  on  Efficiency  of  Utilization  of  Fuel  of  Heating  Air  by 
Mixing  with  Gases  of  Combustion 

Direct  use  of 
gases  of 
Radiated  heat  combustion 

Observations  I  II 

1.  Gallons  of  fuel  per  hour 8.8  6.7 

2.  Average  temperature  of  outside  air....  69°  F.  67°  F. 

3.  Temperature  of  heated  air .' 138.02°  F.  145.2°  F. 

4.  Eise  in  temperature 69°  F.  88°  F. 

5.  Volume    of    air    per    minute    entering 

furnace   roomf 12,800  15,700 

6.  Relative  efficiency  of  use  of  fuel,  using 

volume  of  air  heated,  temperature 
rise  and  fuel  consumption  as  basis 
for  computation  (test  II  taken  as 
100)     67.5%  100% 

When  the  gases  of  combustion  were  used  it  was  found  possible  to 
increase  the  temperature  of  the  air  entering  the  tunnel  to  190°  F. 
without  difficulty.  Temperatures  of  165°  P.  to  175°  F.  were  easily 
maintained. 

*  Calculation  made  by  Mr.  G.  B.  Ridley  from  calorific  value  of  the  fuel,  and 
volume  of  air  heated. 

t  Only  two  cars  were  in  the  tunnel  during  the  test  on  use  of  .  gases  of  com- 
bustion. This  gave  less  resistance  to  air  than  in  first  test  and  accounts  for  greater 
air  flow  and  more  rapid  rate  of  drying. 


Bulletin  322  THE  EVAPORATION  OF  GRAPES  463 

The  data  given  in  the  above  table  are  the  results  of  one  test  only ; 
nevertheless,  a  much  greater  efficiency  for  the  direct  heating  method 
is  indicated.  Further  investigations  will  be  made  upon  this  point 
during  the  coming  season. 

Crude  oil  is  a  much  cheaper  fuel  than  stove  distillate,  but  the  gases 
of  combustion  from  the  former  have  not  been  used  in  drying  because 
of  the  greater  tendency  for  the  formation  of  soot  and  smoke.  Crude 
oil  is,  however,  used  very  commonly  in  furnaces  which  heat  the  air 
by  radiation.  The  question  arises  whether  the  greater  efficiency  of 
the  use  of  the  gases  of  combination  from  the  burning  of  stove  distillate 
will  more  than  compensate  for  the  greater  cost  of  this  fuel,  as  com- 
pared to  the  cost  of  crude  oil  which  is  used  only  in  furnaces  heating 
the  air  by  radiation.  We  do  not  have  sufficient  data  to  answer  this 
question ;  but  it  is  a  point  which  the  builder  of  an  evaporator  must 
carefully  consider. 

(fc)   MOISTURE   CONTENT    OF    EVAPORATED    GEAPES 

The  yield  of  dried  product  varies  in  proportion  to  its  moisture 
content;  this  fact  makes  it  important  for  the  operator  to  know  the 
maximum  percentage  of  water  evaporated  grapes  may  contain  with- 
out becoming  moldy  or  undergoing  fermentation. 

Sixty-one  samples  of  dried  grapes,  including  several  varieties  from 
the  University  Farm  and  from  commercial  evaporators,  and  eighteen 
samples  dried  in  the  laboratory  were  analyzed.  The  average  moisture 
content  of  the  University  Farm  and  commercially  dried  samples  was 
13.83%  ;  the  minimum  was  8.8%,  and  the  maximum,  44.10%.  This 
last  sample  had  fermented  and  the  very  high  moisture  content  indi- 
cated represents  to  a  large  extent  loss  from  alcohol  formed  from  the 
grape  sugar.  The  average  moisture  content  of  the  samples  dried  in 
the  laboratory  was  12.54%. 

A  commercial  sample  containing  30%  moisture  had  undergone 
fermentation  three  months  after  the  date  of  drying,  although  at  one 
month  the  sample  was  free  from  any  evidence  of  fermentation.  Two 
samples  from  the  University  Farm  containing  29.3%  and  33.5% 
moisture,  respectively,  have  not  fermented  or  become  moldy,  but  both 
lots  had  been  heavily  sulfured  before  drying,  which  probably  accounts 
for  their  resistance  to  spoilage.  Several  lots  which  had  not  been  sul- 
fured and  which  contained  25%  to  25.4%  moisture  have  given  no 
evidence  of  decomposition  after  four  months'  storage  in  sealed  con- 
tainers. A  relatively  larger  number  of  samples  containing  between 
20%  and  25%  moisture  have  kept  perfectly.     Therefore,  it  would 


464  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

appear  to  be  safe  to  state  that  grapes  dried  to  24%  or  25%  moisture 
will  not  spoil  and  that  20%  moisture  content  will  certainly  under 
Californian  conditions  not  permit  molding  or  fermentation. 

The  trade  prefers  dried  grapes  that  have  been  stemmed  and  packed 
in  fifty-pound  boxes.  Stemming  can  not  be  satisfactorily  accom- 
plished unless  the  grapes  are  reduced  to  approximately  10%  moisture. 
This  would  necessitate  a  reduction  in  possible  yield  of  10%  to  15% 
through  the  extra  degree  of  drying  necessary  to  permit  stemming. 
However,  in  the  commercial  packing  of  Muscat  raisins  the  moisture 
which  is  removed  from  the  raisins  in  order  to  make  stemming  possible 
is  returned  by  processing  in  hot  water  before  the  raisins  are  passed 
through  the  seeding  machine;  the  final  water  content  of  the  packed 
raisins  being  approximately  16%  to  20%.  Commercial  practice  has 
demonstrated  that  such  fruit  does  not  mold  or  ferment. 

Therefore,  it  should  be  possible  to  return  to  the  stemmed  evaporated 
raisins  enough  water  to  give  in  the  finished  product  that  amount  of 
moisture  which  causes  the  raisins  to  be  of  the  most  desirable  texture ; 
that  is,  about  20%. 

As  the  dried  grapes  come  from  the  evaporator  they  are  not  of  a 
uniform  moisture  content;  some  bunches  will  be  over-dry,  others  too 
wet.  It  is  desirable  to  allow  the  dried  product  to  stand  in  sweat  boxes 
or  bins  for  a  number  of  days  (probably  at  least  two  weeks)  to  permit 
equalization  of  moisture.  This  will  be  particularly  necessary  for 
stemmed  dried  grapes  to  which  water  has  been  added.  Because  of 
the  small  size  of  the  individual  berries,  evaporated  grapes  equalize  in 
water  content  more  rapidly  than  do  the  larger  dried  fruits.  It  was 
observed  that  partially  dried  grapes  from  which  juice  could  still  be 
pressed  easily  gave  up  this  excess  moisture  to  the  drier  grapes  in  the 
sweat  box  before  fermentation  or  molding  could  take  place,  provided 
the  average  moisture  content  of  the  whole  lot  was  not  too  high. 

The  only  method  in  common  use  which  has  proved  accurate  for 
estimating  the  moisture  content  of  dried  grapes  consists  in  drying  a 
weighed  average  sample  of  the  finely  ground  raisins  in  a  vacuum  oven. 
A  temperature  of  90°  C.  (196°  F.)  may  be  used  in  this  determination, 
provided  the  sample  is  not  heated  longer  than  necessary  to  remove 
all  the  water.  Drying  in  an  oven  open  to  the  air  gave  excessively  high 
results  at  all  temperatures  used  because  of  the  loss  in  weight  through 
oxidation  of  the  fruit  sugars.  Preliminary  experiments  indicate  that 
it  is  possible  to  estimate  the  moisture  by  a  simple  method  based  upon 
the  distillation  of  the  sample  with  a  liquid  immiscible  with  water. 
This  method  is  sufficiently  accurate  to  be  very  useful  to  operators  of 
evaporators  for  controlling  the  moisture  content  of  the  dried  product. 


Bulletin  322  THE  evaporation  OP  grapes  465 

(I)   THE  DETERMINATION   OF  HUMIDITY 

The  efficiency  of  an  evaporator  depends  largely  npon  the  degree 
of  saturation  with  moisture  of  the  exhaust  air.  If  the  humidities  of 
the  hot  air  entering  the  drying  tunnel  and  of  the  air  leaving  the 
tunnel  are  measured,  the  amount  of  moisture  absorbed  from  the  fruit 
may  be  easily  calculated  and  the  efficiency  of  the  evaporator  deter- 
mined. Humidity  may  be  determined  by  reading  the  temperature 
of  wet  and  dry  bulb  thermometers  placed  at  the  desired  points  and 
by  use  of  the  following  table.  Explicit  directions  for  use  of  ther- 
mometers and  table  are  given  in  the  discussion  immediately  following 
the  table. 

Two  accurate  Fahrenheit  thermometers  (of  the  variety  known  as 
"chemical  thermometers")  are  the  only  instruments  needed.  Ordi- 
nary dairy  thermometers  reading  to  180°  F.  or  225°  F.  may  be  used 
if  chemical  thermometers  are  not  easily  obtainable.  Most  drug  stores 
carry  thermometers  of  both  types  or  can  obtain  them  on  short  notice. 

Special  instruments  may  be  used  instead  of  the  ordinary  ther- 
mometers. One  known  as  a  "sling  psychrometer"  which  consists  of 
two  thermometers  mounted  side  by  side  on  a  narrow  frame  is  very 
convenient  and  accurate.  Another  instrument  is  so  constructed  that 
humidity  is  read  directly  by  means  of  a  chart  and  pointer  mounted 
upon  the  device  itself.  The  Taylor  Instrument  Company's  Hygrodeik 
is  the  most  common  form  of  this  latter  instrument.  Its  only  fault  is 
that  it  may  be  used  only  for  temperatures  up  to  120°  F. 

Around  the  mercury  bulb  of  one  of  the  thermometers  wrap  a  small 
piece  of  cheese  cloth  of  five  thicknesses  and  extending  about  one-half 
inch  above  the  bulb.  Be  sure  all  of  the  bulb  is  covered  with  the  cloth. 
Tie  the  cloth  with  thread  or  fasten  with  small  rubber  band. 

Dip  the  thermometer  with  the  cloth-covered  bulb  in  water.  Hang 
it  beside  the  other  .plain  thermometer  at  the  point  where  the  test  is  to 
be  made.  Watch  the  two  thermometer  columns  closely.  As  soon  as 
they  remain  at  constant  temperatures  for  about  one  minute  read  both 
carefully.  It  will  usually  require  three  to  five  minutes  for  the  ther- 
mometers to  come  to  constant  temperature.  Do  not  wait  too  long  as 
the  wet-bulb  cloth  will  then  dry  out  and  the  temperature  will  rise  too 
high.  This  point  is  important.  On  the  other  hand,  do  not  take  this 
reading  too  soon  as  it  will  then  be  too  low.  A  little  experience  will 
render  readings  fairly  accurate.  Now  subtract  the  temperature  of 
the  wet  bulb  from  that  of  the  dry  bulb.  In  the  extreme  left  column 
of  the  table  find  the  temperature  nearest  that  of  the  dry  bulb.    In  the 


466 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Table  8. — Belation  of  Humidity  to  Difference  in  Temperature  of  Wet  and  Dry  Bulb 

Thermometers 

(After  The  Foxboro  Company,  Incorporated,  Foxboro,  Massachusetts,  U.  S.  A.,  catalogue 
101-1,  page  9.) 


Dry 
Bulb 

Difference  Between  Readings  of  Wet  and  Dry  Bulbs  in  Degrees  Fahrenheit 

Dry! 
Bulb 

Deg. 
F. 

1 
95 

2 

90 

3 
86 

4 

81 

5 

77 

6 

72 

7 

6S 

8 
64 

9 
59 

10 

55 

11 

51 

12 

48 

13 

44 

14 

40 

15 
36 

16 

33 

17 

29 

18 

35 

19 

22 

20 

19 

22 

12 

24 

6 

26 

0 

28 
0 

30 

32 

34 

36 

38 

40 

45 

50 

55 

60 

65 

70 

Deg. 
F. 

70 

70 

75 

96 

91 

86 

S2 

78 

74 

70 

66 

62 

58 

54 

51 

47 

44 

40 

37 

34 

30 

27 

24 

18 

12 

7 

1 

0 

75 

80 

96 

91 

87 

S3 

79 

75 

72 

68 

64 

61 

57 

54 

50 

47 

44 

41 

38 

35 

32 

29 

23 

IS 

12 

7 

3 

0 

80 

85 

96 

92 

88 

84 

SO 

76 

73 

70 

66 

63 

59 

56 

53 

50 

47 

44 

41 

38 

35 

32 

27 

22 

17 

13 

8 

4 

0 

0 

85 

90 

96 

92 

89 

85 

SI 

78 

74 

71 

68 

65 

61 

58 

55 

52 

49 

47 

44 

U 

39 

36 

31 

26 

22 

17 

13 

9 

5 

1 

0 

90 

95 

96 

93 

89 

85 

S2 

79 

75 

72 

69 

66 

63 

60 

57 

54 

52 

49 

46 

43 

42 

38 

34 

30 

25 

21 

17 

13 

9 

6 

2 

0 

95 

100 

96 

93 

89 

86 

S3 

80 

77 

73 

70 

68 

65 

62 

59 

56 

54 

51 

49 

46 

44 

41 

37 

33 

28 

24 

21 

17 

13 

10 

7 

4 

100 

105 

97 

93 

90 

87 

83 

80 

77 

74 

72 

69 

66 

63 

60 

58 

55 

53 

50 

48 

46 

44 

40 

36 

32 

28 

23 

20 

16 

13 

11 

8 

0 

105 

110 

97 

93 

90 

87 

84 

81 

7S 

75 

73 

70 

67 

65 

62 

60 

57 

55 

52 

50 

48 

46 

42 

38 

34 

30 

26 

23 

20 

17 

14 

11 

4 

0 

110 

115 

97 

94 

91 

88 

85 

82 

79 

76 

74 

71 

68 

66 

63 

61 

58 

57 

54 

52 

50 

48 

43 

40 

36 

32 

28 

26 

22 

20 

16 

14 

7 

2 

115 

120 

97 

94 

91 

88 

85 

82 

80 

77 

74 

72 

69 

67 

65 

62 

60 

58 

55 

53 

51 

49 

45 

41 

38 

34 

31 

28 

25 

22 

19 

17 

10 

5 

0 

120 

125 

97 

94 

91 

88 

85 

S3 

SO 

78 

75 

73 

70 

68 

66 

63 

61 

59 

57 

54 

52 

50 

47 

43 

40 

36 

33 

30 

27 

24 

22 

19 

13 

7 

2 

0 

125 

130 

97 

94 

91 

89 

86 

S3 

81 

78 

76 

73 

71 

69 

67 

64 

62 

60 

58 

56 

54 

52 

48 

45 

41 

38 

35 

32 

29 

26 

24 

21 

15 

10 

6 

1 

130 

135 

97 

94 

92 

89 

86 

84 

81 

79 

76 

74 

72 

69 

67 

65 

63 

61 

59 

57 

55 

53 

50 

46 

43 

40 

36 

34 

30 

2S 

26 

23 

18 

12 

8 

3 

0 

135 

140 

97 

95 

92 

89 

87 

84 

82 

79 

77 

75 

73 

70 

68 

66 

64 

62 

60 

5S 

56 

54 

51 

47 

44 

41 

38 

35 

32 

30 

27 

25 

19 

14 

10 

5 

2 

140 

145 

98 

95 

93 

90 

87 

84 

82 

80 

78 

75 

73 

71 

69 

67 

65 

63 

61 

59 

57 

55 

52 

4S 

45 

42 

39 

36 

34 

31 

29 

27 

21 

16 

12 

7 

4 

0 

145 

150 

98 

95 

93 

90 

87 

85 

82 

80 

78 

76 

73 

71 

70 

68 

65 

64 

62 

60 

5S 

56 

53 

49 

46 

43 

41 

38 

35 

33 

30 

28 

23 

IS 

13 

9 

5 

2 

150 

155 

98 

95 

93 

90 

87 

85 

83 

81 

79 

76 

74 

72 

70 

68 

66 

64 

63 

61 

59 

57 

54 

50 

47 

44 

42 

39 

37 

34 

32 

30 

24 

19 

15 

11 

7 

4 

155 

160 

98 

95 

93 

90 

88 

85 

S3 

81 

79 

77 

75 

73 

71 

69 

67 

65 

63 

62 

60 

58 

-)5 

51 

48 

46 

43 

40 

38 

35 

33 

31 

25 

21 

16 

12 

9 

6 

160 

165 

98 

95 

93 

91 

88 

86 

84 

82 

SO 

78 

75 

73 

72 

70 

68 

66 

64 

62 

61 

59 

56 

52 

49 

47 

44 

41 

39 

37 

34 

32 

27 

22 

IS 

14 

10 

7 

165 

170 

98 

96 

94 

91 

89 

86 

84 

82 

80 

78 

76 

74 

72 

70 

69 

67 

65 

63 

62 

60 

57 

53 

50 

48 

45 

42 

40 

38 

35 

33 

2S 

23 

19 

15 

12 

9 

170 

175 

98 

96 

94 

91 

89 

86 

84 

82 

81 

79 

76 

74 

73 

71 

69 

67 

66 

64 

62 

61 

58 

54 

51 

49 

46 

43 

41 

39 

36 

34 

29 

25 

20 

17 

13 

10 

175 

180 

98 

96 

91 

92 

89 

87 

85 

83 

81 

79 

77 

75 

73 

72 

70 

68 

66 

64 

63 

61 

58 

55 

52 

50 

47 

44 

42 

40 

37 

35 

30 

26 

21 

IS 

14 

12 

180 

185 

98 

96 

94 

92 

89 

87 

85 

83 

81 

80 

77 

7li 

74 

72 

70 

69 

67 

65 

64 

62 

59 

56 

53 

50 

48 

45 

43 

41 

38 

36 

31 

27 

22 

19 

16 

13 

185 

190 

98 

96 

91 

92 

90 

87 

85 

83 

82 

so 

78 

76 

74 

73 

71 

69 

68 

66 

64 

63 

60 

57 

54 

51 

49 

40 

44 

42 

39 

37 

32 

2S 

24 

20 

17 

14 

190 

topmost  horizontal  row  of  the  table  find  the  difference  in  temperature 
nearest  that  of  difference  in  temperature  between  wet  and  dry-bulb 
thermometers.  Follow  down  the  vertical  column  directly  beneath  this 
difference  in  temperature  until  this  vertical  column  cuts  the  horizontal 
row  opposite  the  dry-bulb  thermometer  temperature.     The  figure  at 


Bulletin  322  THE  EVAPORATION  OF  GRAPES  467 

this  point  of  intersection  is  the  relative  humidity.  An  example  will 
make  this  explanation  clearer: 

Dry-bulb  thermometer,  130°  F. ;  wet-bulb  thermometer,  103°  F. ; 
difference,  27°  F. 

Find  in  the  row  at  head  of  table,  28°  F.  and  follow  down  this 
column  until  the  horizontal  row  to  the  right  of  130°  F.  is  met.  At 
this  point  will  be  found  38,  the  per  cent  relative  humidity. 

To  determine  the  increase  in  humidity  of  air  passing  through  the 
evaporator  determine  the  relative  humidity  of  the  hot  air  entering 
the  evaporator  and  that  of  the  exhaust  air.  Calculate  both  to  the 
same  temperature  by  use  of  the  fact  that  each  27°  F.  drop  in  tempera- 
ture doubles  the  relative  humidity.  The  increase  in  humidity  can  then 
be  calculated. 


(m)   MEASUREMENT  OF  AIR  VELOCITY 

The  rate  of  air  flow  through  the  evaporator  and  especially  over 
the  trays  determines  the  rate  of  drying.  An  instrument  known  as 
an  anemometer,  which  consists  of  a  small  disc  fan  made  up  of  small 
vanes  attached  to  a  pinion  connected  to  several  dials,  is  used  to  meas- 
ure the  velocity  of  air  currents.  It  is  placed  with  the  revolving  vanes 
facing  the  air  current.  The  "hundreds"  dial  is  read.  The  clutch 
is  released  and  the  instrument  allowed  to  run  for  exactly  one  minute 
and  the  dials  read  again.  The  difference  between  first  and  second 
reading  of  "hundreds"  dial  gives  the  velocity  of  the  air  in  hundreds 
of  feet  per  minute,  ,  The  velocity  should  be  in  a  horizontal  blast 
evaporator  at  least  300  feet  per  minute  over  the  trays  at  the  exhaust 
end  of  the  tunnel.  It  should  be  possible  to  reach  500  feet  per  minute 
at  this  point  if  the  evaporator  has  been  properly  designed  and  built. 

Anemometers  may  be  had  from  chemical  supply  houses  or  from 
dealers  in  heating  and  ventilating  equipment.  The  one  used  by  the 
University  cost  twenty-five  dollars.  The  Pitot  tube  is  an  instrument 
used  to  measure  static  pressure  in  the  drying  tunnel  and  is  a  useful 
check  for  the  anemometer. 


O)   EXPERIMENTS   ON   STEMMING,    SEEDING   AND   PACKING 

In  order  that  evaporated  grapes  may  be  stemmed  successfully 
they  must  be  dried  to  a  moisture  content  of  about  10  per  cent  or  less 
and  must  be  transferred  to  the  stemming  machine  within  a  short  time 
(a  few  hours)  after  the  grapes  emerge  from  the  evaporator.  They  are 
at  this  time  very  dry  on  the  surface  and  for  a  short  distance  into  the 


468 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


flesh,  a  condition  which  gives  sufficient  rigidity  to  the  berries  to  permit 
stemming.  After  standing  over  night  the  moisture  near  the  center  of 
the  raisins  diffuses  toward  the  surface  and  moisture  is  absorbed  from 
the  air,  causing  them  to  become  so  soft  and  pliable  that  stemming  is 
difficult.  The  stems  of  freshly  dried  grapes  are  dry  and  brittle  but 
after  a  few  hours '  standing  become  wiry  and  difficult  to  remove  in  the 
stemmer. 

A  test  was  made  at  a  commercial  evaporator  to  determine  the  loss 
in  weight  during  stemming.  Two  hundred  and  eighty  pounds  of  over- 
dried  Alicante  Bouschet  grapes  were  passed  through  a  cleaned  stem- 
ming machine.  Stemming  was  very  satisfactory,  but  few  grapes  being 
lost  with  the  stems.  The  weight  of  the  stems  removed  was  5.7  per  cent. 
The  raisins  were  not  passed  through  a  cap  stemmer  although  many  of 
the  cap  stems  were  removed.  These  grapes  had  been  gathered  in  such 
a  manner  that  pieces  of  cane  four  to  six  inches  long  were  left  on  many 
of  the  bunches.  This  would  probably  cause  the  loss  in  weight  during 
stemming  to  be  higher  than  the  average  for  grapes  picked  in  the  usual 
manner  and  this  figure  should  therefore  be  a  conservative  one  for  the 
calculation  of  loss  due  to  stemming  dried  wine  grapes  under  average 
conditions. 

Through  the  cooperation  of  L.  R.  Payne  of  the  California  Asso- 
ciated Raisin  Company  of  Fresno  stemming  and  seeding  tests  were 
made  at  the  Fresno  plant  of  the  above  company  upon  small  lots  of 
dried  Petite  Sirah,  Semillon,  and  Muscat  grapes.  The  following  table 
contains  the  results  of  Mr.  Payne's  tests.  Because  the  lots  were  so 
small  the  results  on  losses  during  stemming  and  seeding  are  exces- 
sively high,  but  are  still  of  value  for  comparison  with  losses  in  stem- 
ming and  seeding  Muscat  raisins  under  the  same  conditions.  The 
results  given  below  do  not  take  into  account  the  water  returned  to  the 
fruit  before  seeding. 

Table  9. — Losses  During  Stemming  and  Seeding  Evaporated  Grapes. 


Muscat, 

Observations  per  cent 

1.  Stemmer  loss   13.69 

2.  Drier   loss   2.4 

3.  Loss   in    seeding 10.46 

4.  Total    loss    in    stemming 

and  seeding  24.05 


Semillon 

(white  wine 

grapes), 

per  cent 

Petite  Sirah 
(red  wine 
grapes), 
per  cent 

Sultanina 

(Thompson 

seedless), 

per  cent 

7.81 

13.39 

10.20 

7.4 

10 

10.5 

16 

31.11 

23.81 

44.50 

10.20 
(seedless) 

Bulletin  322  THE  EVAPORATION  OF  GRAPES  469 

The  results  indicate  that  the  loss  in  seeding  of  dried  wine  grapes 
whose  berries  are  above  the  average  in  size  is  not  much  greater  than 
that  of  Muscat  raisins,  while  the  loss  in  seeding  dried  wine  grapes 
with  small  berries  (Petite  Sirah)  is  about  three  times  that  of  Muscat 
raisins.  The  tests  at  least  indicated  that  it  is  possible  to  remove  the 
seeds  from  such  dried  grapes,  although  it  is  doubtful  whether  such 
a  product  could  be  produced  as  economically  as  seeded  Muscat  raisins. 

The  seeded  Petite  Sirah  raisins  were  of  excellent  flavor  and  prac- 
tically free  from  pieces  of  broken  seeds.  Tests  were  made  of  their 
suitability  for  culinary  use.  Pies  made  from  them  resembled  black- 
berry pies  in  flavor,  color  and  general  appearance.  A  slightly 
astringent  flavor  was  noticeable  if  the  dried  grapes  alone  were  used 
but  this  defect  was  overcome  when  the  raisins  were  mixed  with  an 
equal  quantity  of  chopped  apples.  These  raisins  will  give  excellent 
results  in  various  puddings,  cookies,  cakes,  and  candy  in  which  they 
may  be  used  to  replace  Muscat  raisins  in  the  usual  recipes. 

If  seeded  dried  red  wine  grapes  can  be  produced  and  sold  for  a 
price  not  greatly  in  excess  of  that  received  for  Muscat  or  seedless 
raisins  it  should  be  possible  to  develop  an  extensive  market  for  them. 

During  the  past  season  the  dried  grapes  were  sold  in  the  un- 
stemmed  condition  in  sacks  and  boxes  by  some  producers;  others 
packed  the  stemmed  unseeded  product  in  fifty-pound  boxes.  These 
latter  brought  the  best  prices  and  it  is  probable  that  this  method  of 
packing  will  be  adopted  generally  in  the  future. 

The  machines  used  for  stemming  muscat  raisins  have  proved  satis- 
factory for  dried  wine  grapes,  although  as  previously  stated  the  raisins 
must  be  thoroughly  dry  if  satisfactory  results  are  to  be  obtained. 

VII.      SUMMARY 

1.  An  evaporator  of  the  horizontal  tunnel  air-blast  type  and  of 
six  tons  of  fresh  fruit  capacity  per  charge  was  constructed  on  the 
University  Farm  at  Davis  during  1919  by  funds  furnished  by  the 
State  Board  of  Viticultural  Commissioners  and  the  University.  This 
evaporator  was  used  successfully  in  the  drying  of  grapes  and  prunes. 
Plans,  cost,  and  general  specifications  of  this  evaporator  are  to  be 
found  in  the  text  of  this  publication.  Sketches  indicating  revised 
evaporator  plans  recommended  to  growers  have  been  given.  The 
recommended  evaporator  is  of  the  same  capacity  and  general  appear- 
ance as  the  University  Farm  evaporator  but  embodies  the  improve- 
ments which  we  have  found  desirable  to  increase  the  efficiency  of  the 
plant.     The  evaporator  can  be  constructed  for  about  $3,500.     We 


470  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

believe  the  recommended  evaporator  to  be  equal  in  efficiency  to  any 
evaporator  of  similar  capacity  now  in  use  and  superior  to  many.  It 
is  not  expensive  to  construct  and  can  be  erected  by  local  artisans. 

Most  of  the  suggested  improvements  are  now  being  made  in  our 
plant.  Therefore,  growers  who  contemplate  the  erection  of  evapora- 
tors are  urged  to  visit  the  University  Farm. 

2.  Dipping  of  grapes  in  a  dilute  boiling  lye  solution  approximately 
doubled  the  rate  of  drying.  Most  wine-grape  varieties  and  Muscat 
grapes  require  a  lye  solution  of  2%  to  3%  for  effective  results. 
Tokays  and  Thompson  Seedless  require  only  a  %%  solution. 

3.  Grapes  dried  in  the  evaporator  were  improved  by  a  short  period 
of  sulfur ing  before  drying.  Much  less  sulfur ing  was  required  for 
grapes  dried  in  the  evaporator  than  for  those  dried  in  the  sun. 

4.  No  definite  constant  difference  in  yield  could  be  found  in  sun- 
drying  and  evaporation.  The  color  and  flavor  of  the  juice  obtained 
by  soaking  sun-dried  grapes  in  water  was  much  inferior  to  juice 
obtained  from  evaporated  grapes. 

5.  The  rate  of  drying  is  greatly  increased  by  increase  in  tempera- 
ture of  the  air  used  in  drying.  Temperatures  up  to  190°  F.  were 
used  successfully  on  red-wine  grapes,  although  it  was  found  necessary 
to  remove  the  grapes  from  the  evaporator  as  soon  as  dry,  to  avoid 
injury  to  color  and  flavor.  A  temperature  of  165°  F.  may  be  used 
in  regular  practice. 

6.  Recirculation  of  a  large  proportion  of  the  exhaust  air  from 
the  evaporator  greatly  reduces  fuel  consumption  without  reduction 
of  the  rate  of  drying.  Recirculation  prevents  overdrying  of  the  fruit 
and  permits  regulation  of  moisture  content  of  the  dried  product.  It 
is  believed  that  higher  temperatures  of  drying  may  be  employed  where 
the  humidity  of  the  air  used  in  drying  is  increased  by  recirculation. 

7.  The  suction  type  of  fan  proved  more  satisfactory  than  the  blast 
type.  The  multivane  fan  was  found  to  be  much  more  efficient  than 
the  disc  type. 

8.  The  air-blast  distillate  burner  was  more  satisfactory  than  the 
gravity  burner,  although  both  were  used  successfully. 

9.  Dried  grapes  of  25%  or  less  moisture  have  kept  perfectly;  those 
of  30%  or  over  have  spoiled  unless  heavily  sulfured.  The  dried 
product  equalized  rapidly  in  moisture  content  in  sweat  boxes. 

10.  Dried  grapes  stemmed  satisfactorily  when  dried  to  about  10% 
moisture  and  stemmed  within  a  few  hours  after  drying. 


Bulletin  322  THE  EVAPORATION  OF  GRAPES  471 

11.  The  dried  grapes  adhered  with  great  tenacity  to  screen  trays 
but  were  easily  removed  from  slat-bottom  trays.  Grapes  dried  as 
rapidly  on  the  latter  as  on  the  former.  The  slat-bottom  trays  are  of 
greater  durability  and  lower  cost  than  screen  trays. 

12.  Dried  wine  grapes  were  seeded  successfully  but  the  loss  during 
this  process  was  excessively  large.  The  seeded  product  gave  excellent 
results  when  used  for  pies,  puddings  and  other  dishes.  Dried  white 
wine  grapes  gave  fair  results  on  seeding  but  the  finished  product  was 
inferior  to  Muscat  raisins.  Seeded  dried  wine  grapes  appear  to  have 
possibilities  for  culinary  use. 

13.  Evaporator  manufacturers.  A  list  of  manufacturers  of  evapo- 
rators and  dealers  in  evaporator  equipment  will  be  sent  on  request 
made  to  the  Division  of  Viticulture  and  Fruit  Products. 

14.  Nomenclature.  At  the  present  time  various  terms  are  applied 
more  or  less  indiscriminately  to  fruits  and  vegetables  from  which  most 
of  the  water  has  been  removed  in  order  to  preserve  the  product.  At  a 
convention  held  in  San  Jose  on  evaporation  a  committee  consisting  of 
A.  W.  Christie,  Paul  F.  Nicholls,  E.  M.  Sheehan,  H.  C.  Rowley,  and 
S.  C.  Simons  was  .appointed  to  consider  this  question.  The  committee's 
report,  which  has  been  approved  by  the  College  of  Agriculture  through 
a  committee  consisting  of  J.  C.  Whitten,  M.  E.  Jaffa,  W.  V.  Cruess, 
E.  L.  Overholser,  and  J.  P.  Bennet  is  as  follows  : 

a.  The  same  nomenclature  shall  be  applied  to  fruits  and  vege- 
tables. 

b.  The  term  " dried"  is  applied  to  all  fruits  and  vegetables  pre- 
served by  the  removal  of  moisture,  irrespective  of  the  method  of 
removal. 

c.  There  are  but  two  classes  of  dried  fruits  and  vegetables,  namely, 
those  dried  principally  by  solar  heat  and  those  dried  principally  by 
artificial  heat. 

d.  The  class  dried  principally  by  solar  heat  shall  be  designated 
' '  sun-dried, ' '  by  which  is  meant  the  removal  of  moisture  by  solar  heat 
without  control  of  temperature,  humidity,  or  air  flow. 

e.  The  class  dried  principally  by  artificial  heat  shall  be  designated 
either  "evaporated"  or  "dehydrated."  The  committee  finds  at  this 
time  no  sufficient  reasons  for  distinguishing  between  "evaporated" 
and  "dehydrated." 


STATION  PUBLICATIONS  AVAILABLE  FOR  FREE  DISTRIBUTION 


No. 
168. 

169. 
185. 

208. 
230. 
250. 
251. 


252. 
253. 


257. 
261. 

262. 


263. 
266. 


267. 

268. 
270. 


271. 
272. 
273. 

274. 

275. 

276. 

277. 
278. 
279. 
280. 

281. 

282. 


Observations  on  Some  Vine  Diseases 
in   Sonoma   County. 

Tolerance  of  the  Sugar  Beet  for  Alkali. 

Report  of  Progress  in  Cereal  Investi- 
gations. 

The  Late  Blight  of  Celery. 

Enological  Investigations. 

The  Loquat. 

Utilization  of  the  Nitrogen  and  Organic 
Matter  in  Septic  and  Imhoff  Tank 
Sludges. 

Deterioration  of  Lumber. 

Irrigation  and  Soil  Conditions  in  the 
Sierra   Nevada   Foothills,    California. 

New   Dosage   Tables. 

Melaxuma  of  the  Walnut,  "Juglans 
regia." 

Citrus  Diseases  of  Florida  and  Cuba 
Compared  with  Those  of  California. 

Size  Grades  for  Ripe  Olives. 

A  Spotting  of  Citrus  Fruits  Due  to  the 
Action  of  Oil  Liberated  from  the 
Rind. 

Experiments  with  Stocks  for  Citrus. 

Growing  and  Grafting  Olive  Seedlings. 

A  Comparison  of  Annual  Cropping,  Bi- 
ennial Cropping,  and  Green  Manures 
on  the  Yield  of  Wheat. 

Feeding  Dairy  Calves  in  California. 

Commercial  Fertilizers. 

Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain. 

The  Common  Honey  Bee  as  an  Agent 
in  Prune  Pollination. 

The  Cultivation  of  Belladonna  in  Cali- 
fornia. 

The  Pomegranate. 

Sudan  Grass. 

Grain   Sorghums. 

Irrigation  of  Rice  in  California. 

Irrigation  of  Alfalfa  in  the  Sacramento 
Valley. 

Control  of  the  Pocket  Gopher  in  Cali- 
fornia. 

Trials  with  California  Silage  Crops  for 
Dairy  Cows. 


BULLETINS 

No. 
283. 
285. 
286. 
288. 


290. 

293. 
296. 
297. 
298. 
299. 

300. 
301. 

302. 

303. 
304. 

305. 

307. 

308. 


309. 

310. 
311. 
312. 
313. 

314. 
316. 
317. 

318. 
319. 
320. 
321. 
322. 


The  Olive  Insects  of  California. 

The  Milch  Goat  in  California. 

Commercial  Fertilizers. 

Potash  from  Tule  and  the  Fertilizer 
Value  of  Certain  Marsh  Plants. 

The  June  Drop  of  Washington  Navel 
Oranges. 

Sweet   Sorghums  for  Forage. 

Topping   and   Pinching  Vines. 

The  Almond  in  California. 

Seedless  Raisin   Grapes. 

The  Use  of  Lumber  on  California 
Farms. 

Commercial  Fertilizers. 

California  State  Dairy  Cow  Competi- 
tion,  1916-18. 

Control  of  Ground  Squirrels  by  the 
Fumigation  Method. 

Grape  Syrup. 

A  Study  on  the  Effects  of  Freezes  on 
Citrus  in  California. 

The  Influence  of  Barley  on  the  Milk 
Secretion  of  Cows. 

Pollination  of  the  Bartlett  Pear. 

I.  Fumigation  with  Liquid  Hydrocianic 
Acid.  II.  Physical  and  Chemical 
Properties  of  Liquid  Hydrocianic 
Acid. 

I.  The  Carob  in  California.  II.  Nutri- 
tive Value  of  the  Carob  Bean. 

Plum  Pollination. 

Investigations  with  Milking  Machines. 

Mariout  Barley. 

Pruning  Young  Deciduous  Fruit 
Trees. 

Cow-Testing  Associations  in  California. 

The  Kaki  or  Oriental  Persimmon. 

Selection  of  Stocks  in  Citrus  Propoga- 
tion. 

The  Effects  of  Alkali  on  Citrus  Trees. 

Caprifigs  and  Caprification. 

Control  of  the  Coyote  in  California. 

Commercial  Production  of  Grape  Syrup. 

The  Evaporation  of  Grapes. 


No. 

50. 
65. 

70. 

76. 
82. 

87. 
109. 


110. 
111. 

113. 
114. 
115. 
117. 

124. 
126. 
127. 
128. 
129. 
130. 
131. 
133. 


Fumigation   Scheduling. 

The  California  Insecticide  Law. 

Observations  on  the  Status  of  Corn 
Growing  in  California. 

Hot  Room  Callusing. 

The  Common  Ground  Squirrels  of 
California. 

Alfalfa. 

Community  or  Local  Extension  Work 
by  the  High  School  Agricultural  De- 
partment. 

Green  Manuring  in  California. 

The  Use  of  Lime  and  Gypsum  on  Cali- 
fornia  Soils. 

Correspondence  Courses  in  Agriculture. 

Increasing  the  Duty  of  Water. 

Grafting  Vinifera  Vineyards. 

The  Selection  and  Cost  of  a  Small 
Pumping  Plant. 

Alfalfa  Silage  for  Fattening  Steers. 

Spraying  for  the  Grape  Leaf  Hopper. 

House  Fumigation. 

Insecticide  Formulas. 

The  Control  of  Citrus  Insects. 

Cabbage  Growing  in  California. 

Spraying  for  Control  of  Walnut  Aphis. 

County  Farm  Adviser. 


CIRCULARS 
No. 
135. 
136. 
137. 
138. 
139. 


140. 


143. 

144. 
147. 
148. 
152. 

153. 

154. 

155. 
156. 
157. 
158. 
159. 
160. 


Official  Tests  of  Dairy  Cows. 

Melilotus  Indica. 

Wood  Decay  in  Orchard  Trees. 

The  Silo  in  California  Agriculture. 

The  Generation  of  Hydrocyanic  Acid 
Gas  in  Fumigation  by  Portable 
Machines. 

The  Practical  Application  of  Improved 
Methods  of  Fermentation  in  Califor- 
nia Wineries  during  1913  and  1914. 

Control  of  Grasshoppers  in  Imperial 
Valley. 

Oidium  or  Powdery  Mildew  of  the  Vine. 

Tomato  Growing  in  California. 

"Lungworms". 

Some  Observations  on  the  Bulk  Hand- 
ling of  Grain  in  California. 

Announcement  of  the  California  State 
Dairy  Cow  Competition,   1916-18. 

Irrigation  Practice  in  Growing  Small 
Fruits  in  California. 

Bovine  Tuberculosis. 

Plow  to  Operate  an  Incubator. 

Control  of  the  Pear  Scab. 

Home  and  Farm   Canning. 

Agriculture  in  the  Imperial  Valley. 

Lettuce  Growing  in  California. 


CIRCULA  RS— Continued 


No.  No. 

164.  Small   Fruit   Culture  in   California.  191. 

165.  Fundamentals   of    Sugar    Beet   Culture  193. 

under  California  Conditions.  195. 

167.  Feeding  Stuffs  of  Minor  Importance. 

168.  Spraying     for     the     Control     of     Wild  197. 

Morning-Glory  within   the  Fog  Belt. 

169.  The    1918   Grain   Crop.  198. 

170.  Fertilizing     California     Soils     for     the  199. 

1918   Crop.  201. 

172.  Wheat  Culture.  202. 
173     The    Construction    of    the    Wood-Hoop 

Silo.  203. 

174.  Farm  Drainage  Methods.  204. 

175.  Progress  Report  on  the  Marketing  and 

Distribution   of  Milk.  205. 

176.  Hog  Cholera  Prevention  and  the  Serum  206. 

Treatment.  207. 

177.  Grain    Sorghums.  208. 

178.  The  Packing  of  Apples  in  California. 

179.  Factors    of     Importance    in    Producing  209. 

Milk   of  Low  Bacterial   Count.  210. 

181.  Control     of      the     California     Ground  213. 

Squirrel.  214. 

182.  Extending  the  Area  of  Irrigated  Wheat 

in   California  for   1918.  215. 

183.  Infectious  Abortion  in   Cows.  216. 

184.  A  Flock  of  Sheep  on  the  Farm. 

185.  Beekeeping    for    the    Fruit-grower    and  217. 

Small  Rancher  or  Amateur. 

187.  Utilizing  the   Sorghums.  218. 

188.  Lambing  Sheds. 

189.  Winter  Forage  Crops.  219. 

190.  Agriculture  Clubs  in   California. 


Pruning  the  Seedless  Grapes. 

A  Study  of  Farm  Labor  in  California. 

Revised  Compatibility  Chart  of  Insecti- 
cides and  Fungicides. 

Suggestions  for  Increasing  Egg  Produc- 
tion in  a  Time  of  High-Feed  Prices. 

Syrup  from  Sweet  Sorghum. 

Onion   Growing  in   California. 

Helpful   Hints  to  Hog  Raisers. 

County  Organization  for  Rural  Fire 
Control. 

Peat   as   a  Manure   Substitute. 

Handbook  of  Plant  Diseases  and  Pest 
Control. 

Blackleg. 

Jack  Cheese. 

Neufchatel   Cheese. 

Summary  of  the  Annual  Reports  of  the 
Farm  Advisors  of  California. 

The  Function  of  the  Farm  Bureau. 

Suggestions  to  the  Settler  in  California. 

Evaporators  for  Prune  Drying. 

Seed  Treatment  for  the  Prevention  of 
Cereal  Smuts. 

Feeding-  Dairy  Cows  in  California. 

Winter  Injury  or  Die-Back  of  the  Wal- 
nut. 

Methods  for  Marketing  Vegetables  in 
California. 

Advanced  Registry  Testing  of  Dairy 
Cows. 

The  Present  Status  of  Alkali. 


